Re: [MF3D-group] Re: A properly designed MF viewer.

Subject: Re: getting this for the TL120
Date: 2008-07-11 19:33:20
From: Harry Calderbank

--- In MF3D-group@yahoogroups.com, "Mark" wrote:

>
> Hi
>
> had a go with the little light thing last night at a spoken word

club

> - angle of it didn't illuminate squat.
>
> So either I wear them or not sure what.
>
> Least its not the Sputnik so should be easier to handle in near dark

For anyone wanting to shoot in the dark with the TL120, I would think
it would be possible to memorise the number of winds needed from the
start of the film. If you can get the film loaded and ready to shoot
on the first frame, you could probably be able to remember the number
of winds needed to advance the film to the next pair of frames. I
haven't needed to do a whole shoot like this myself, but I know that
the first wind needs about eight and a half cranks to get it to the
next pair. This decreases with each subsequent pair until the last
pair where I generally need just under seven cranks. Naturally the
number alters as the take up spool gets thicker. I would think that
with a bit of practice, you could get to memorise the right number of
cranks needed (along with remembering where you are up to on the
film) to successfully shoot a whole film without looking at the back
of the camera. As I said, I haven't tried this myself yet with a
whole film but I have used a quick eight cranks between two shots
that I needed in a real hurry and it worked well enough. I will try
memorising what is needed for a whole film for each shot when I shoot
my next roll - so long as I remember to write it down! It may well
vary a little depending on the film used as some seem to have
differing thicknesses and lengths of paper leader. It might be worth
a try if you regularly intend to shoot in the dark and don't want to
use a light or torch.

regards

Harry Calderbank

Subject: advancing film in the TL120 by count [was: getting this for the TL12
Date: 2008-07-11 21:35:46
From: John Thurston

Harry Calderbank wrote:

> --- In MF3D-group@yahoogroups.com, "Mark"
> wrote:
>> Hi
>>
>> had a go with the little light thing last night at a
>> spoken word
> club
>> - angle of it didn't illuminate squat.
>>
>> So either I wear them or not sure what.
>>
>> Least its not the Sputnik so should be easier to handle
>> in near dark
>
> For anyone wanting to shoot in the dark with the TL120, I
> would think it would be possible to memorise the number of
> winds needed from the start of the film. If you can get
> the film loaded and ready to shoot on the first frame, you
> could probably be able to remember the number of winds
> needed to advance the film to the next pair of frames.

The film gates on the TL120 are so wide that the allowable
error in film advance is very small. Even in daylight and
with care in the advance of the film, I sometimes overlap my
frames.

If you are going to try the "advance by count" routine, as
you count your trial roll, I suggest you start your roll
"short" and plan on ending it "long". That is, expose your
first image nearer the start of the film (just before the "1"
is in the window) and kind of let the frame number walk
across the red window as you shoot subsequent images. Shoot
your last image as the "11" is just past the window. This
will expand the inter-image spacing and reduce the chance for
overlap. Looking at one of your processed rolls will give you
an indication of how much film you have to play with at each end.
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us

Subject: Re: getting this for the TL120
Date: 2008-07-11 23:57:29
From: Michael Kersenbrock

Mark wrote:

> Hi
>
> had a go with the little light thing last night at a spoken word club
> - angle of it didn't illuminate squat.
>
> So either I wear them or not sure what.
>
> Least its not the Sputnik so should be easier to handle in near dark
>

And that's the truth! I once tried night photography with my Sputnik on
the Vegas
Strip. First photo wasn't too bad, but advancing the film properly was
nearly a miracle.

Mike K.

Subject: Re: getting this for the TL120
Date: 2008-07-12 09:32:56
From: dlopp2000

Does the TL-120 camera still contain a red window ?

If so, can anyone offer a valid reason for not using a
plain, clear window ?

Incidentally, a few years ago, Dick Twitchell, used 220
film in his Sputnik. It was outdated film at a very low
cost. He counted the revolution turns of his film wind
knob. Dick did not get as many exposures as he should
have if using a standard film advance, but overall it was
very cost effective.

DON

Subject: Re: getting this for the TL120
Date: 2008-07-12 10:20:51
From: Dan Vint

At 08:32 AM 7/12/2008, you wrote:

>Incidentally, a few years ago, Dick Twitchell, used 220
>film in his Sputnik. It was outdated film at a very low
>cost. He counted the revolution turns of his film wind
>knob. Dick did not get as many exposures as he should
>have if using a standard film advance, but overall it was
>very cost effective.

When in doubt roll to far. Its better to waste film than it is to
loose that killer image you just got the one time opportunity to get.

The red window is to kill some of the light getting into the camera,
you might have a greater chance of fogging the film, especially with
the window open all the time and out in bright light. With B&W
processing you can use a red safe light in a dark room, but other
colors and brighter values would fog the film.

..dan
---------------------------------------------------------------------------
Danny Vint

Specializing in Panoramic Images of California and the West
http://www.dvint.com

voice: 510-522-4703

When H.H. Bennett was asked why he preferred to be out
shooting landscapes rather than spending time in his portrait studio:

"It is easier to pose nature and less trouble to please."

http://www.portalwisconsin.org/bennett_feature.cfm

Subject: Re: getting this for the TL120
Date: 2008-07-13 02:23:56
From: Mark

Hi

One thing that bugs me about the TL120 is that you still need to look
at the window and wind. Even on my Kiev88 you don't need to do that
once its set at one.

Slows down shooting and will now attach a light to the strap as I was
caught in a darker environment on fri night. Try using a candle to
advance frames!

M

Subject: Re: getting this for the TL120
Date: 2008-07-14 21:40:08
From: dlopp2000

Recently i asked the following questions, but did not
receive a serious answer.

> Does the TL-120 camera still contain a red window ?

> If so, can anyone offer a valid reason for not using a
> plain, clear window ?

According to Mr Calderbank, the TL-120 does contain a red
window.

I am still waiting to read of a valid reason for the contin-
ued use of the red window system, in this year of 2008.

DON

Subject: red window [was: getting this for the TL120]
Date: 2008-07-14 22:00:11
From: John Thurston

dlopp2000 wrote:

> According to Mr Calderbank, the TL-120 does contain a red
> window.
>
> I am still waiting to read of a valid reason for the contin-
> ued use of the red window system, in this year of 2008.

There ain't no valid reason, Don. It's just expected.
Like an "ATM machine", a "PIN number" or an "SAT test", a chunk of
red plastic is stuck in the window even though it makes no sense.

John Thurston
Juneau, Alaska

Subject: Re: getting this for the TL120
Date: 2008-07-14 23:41:28
From: Michael Kersenbrock

dlopp2000 wrote:

>
> I am still waiting to read of a valid reason for the contin-
> ued use of the red window system, in this year of 2008.
>
>

Good point. It probably should have a little film pattern detector
of some sort with an LCD screen showing digitally what STEREO
exposure number is being used (but of course, it won't be lit
so it'll still be hard as heck to see in the dark). :-)

Mike K.

Subject: Re: getting this for the TL120
Date: 2008-07-15 01:00:04
From: Jeremy McGee

I thought the purpose of the red window was to decrease the chance of light leaks.

Michael Kersenbrock wrote:

dlopp2000 wrote:
>
> I am still waiting to read of a valid reason for the contin-
> ued use of the red window system, in this year of 2008.
>
>

Good point. It probably should have a little film pattern detector
of some sort with an LCD screen showing digitally what STEREO
exposure number is being used (but of course, it won't be lit
so it'll still be hard as heck to see in the dark). :-)

Mike K.

Subject: Re: getting this for the TL120
Date: 2008-07-15 02:39:48
From: Jeremy McGee

Meant to include the word "historically". By that I mean that the red window is simply a sentimental decorative touch.

Jeremy McGee wrote:

I thought the purpose of the red window was to decrease the chance of light leaks.

Michael Kersenbrock wrote:

dlopp2000 wrote:
>
> I am still waiting to read of a valid reason for the contin-
> ued use of the red window system, in this year of 2008.
>
>

Good point. It probably should have a little film pattern detector
of some sort with an LCD screen showing digitally what STEREO
exposure number is being used (but of course, it won't be lit
so it'll still be hard as heck to see in the dark). :-)

Mike K.

Subject: Re: red window [was: getting this for the TL120]
Date: 2008-07-15 09:40:06
From: Chuck Holzner

> dlopp2000 wrote:
> > According to Mr Calderbank, the TL-120 does

contain a red

> > window.
> >
> > I am still waiting to read of a valid reason

for the contin-

> > ued use of the red window system, in this

year of 2008.

>

It seems that at least one person in this group
find the RED window used for film advancement in
the TL-120 objectionable. Apparently, mostly
because it is in the traditional color of RED.

Some solutions to this "problem" could be:

1: The manufacturer could make the window
available in different colors. No doubt it could
be made in most any color of choice and so it
could be a custom item.
2) The color window could be replaceable much
like lens filters. Different colors and shades
could be made and it would be easy to replace
them with the filter of your choice. Maybe even
stack filters. Lenses with correction could be
available to correct for the users eyesight.
3) A mechanical counter coupled with a friction
wheel on the film could be used to measure the
film movement and stop the advance when needed.
This would eliminate the need for the window and
allow the use of 220 size film doubling the
number of shots taken between film loadings.
4) In this modern year of 2008, no doubt, a
counter wheel could be coupled electronically and
advance a counter that would indicate how far the
film had advanced. It could be used to stop an
electric film advance that was started when the
shutter closed and would assure proper film
advancement in total darkness as well as assure
the film was advanced for each shot to prevent
double exposures.

All of these improvements could be incorporated
at some increase in cost. Of course some people
just may opt for less expense and a traditional
RED window.

Chuck Holzner

Subject: Re: red window [was: getting this for the TL120]
Date: 2008-07-15 14:43:23
From: Brian Reynolds

Chuck Holzner wrote:

> > dlopp2000 wrote:
> > > According to Mr Calderbank, the TL-120 does contain a red
> > > window.
> > >
> > > I am still waiting to read of a valid reason for the continued
> > > use of the red window system, in this year of 2008.
>
> It seems that at least one person in this group
> find the RED window used for film advancement in
> the TL-120 objectionable. Apparently, mostly
> because it is in the traditional color of RED.

The point is that for a panchromatic film (technically a B&W film, but
color slide film is certainly sensitive to the full spectrum) a red
window is no less likely to cause light leaks than a clear window.
Back when people used orthochromatic B&W film a red window made sense
because the film wasn't sensitive to the red light that the window let
through.

> Some solutions to this "problem" could be:
>

[snip]

> 3) A mechanical counter coupled with a friction
> wheel on the film could be used to measure the
> film movement and stop the advance when needed.
> This would eliminate the need for the window and
> allow the use of 220 size film doubling the
> number of shots taken between film loadings.
>
> 4) In this modern year of 2008, no doubt, a
> counter wheel could be coupled electronically and
> advance a counter that would indicate how far the
> film had advanced. It could be used to stop an
> electric film advance that was started when the
> shutter closed and would assure proper film
> advancement in total darkness as well as assure
> the film was advanced for each shot to prevent
> double exposures.

With regards to 3 & 4, when Keith Canham was first designing his
motorized 6x17 rollfilm back he told me that it was motorized (and the
advance was monitored by a microcontroller) because that was cheaper
than designing and building a geared advance.

> All of these improvements could be incorporated
> at some increase in cost. Of course some people
> just may opt for less expense and a traditional
> RED window.

A clear window would allow people to more easily see the frame
numbers, and traditionalists could simply tape some red cellophane to
the inside of the camera back.

--
Brian Reynolds | "It's just like flying a spaceship.
reynolds@panix.com | You push some buttons and see
http://www.panix.com/~reynolds/ | what happens." -- Zapp Brannigan
NAR# 54438 |

Subject: Re: getting this for the TL120
Date: 2008-07-15 16:21:25
From: dlopp2000

I recently asked:

Can anyone offer a valid reason for not using a
plain, clear window ?

Apparently, there is not a valid reason for not
using a plain clear window.

I have used both a Rolleidoscop and a Heidoscop
camera.

Both cameras utilized a red window which was about
3 inches in width.

For reasons unknown to me, the cameras were not de-
signed to be used with 120 film, and would only offer
5 stereo pairs per roll of 120 film.

After removing the red celluloid window, I was able
re-index the back of the cameras, allowing me to
produce 6 stereo pairs on a roll of 120 film, which
required a film advance that was accurate to within
1/16th of an inch. The numbers on the back of each
roll of 120 film allowed this degree of accuracy.

My experience has shown that the opaque black paper
backing on consumer level color slide film, Kodak and
Fuji, can withstand 4+ hours of exposure to direct
sunlight.

There were, and are many roll film cameras, (Hasselblad,
Kodak, Rollei, Ansco, Hasselblad, Fuji, Mamiya, Bronica,
etc), that allow a precision film advance without using
a red window, when advancing the film.

The patents have expired, and I see no reason to re-invent
the wheel.

IMO, only Brian has offered a viable solution.

DON

>

Subject: Re: getting this for the TL120
Date: 2008-07-15 16:48:02
From: John Thurston

dlopp2000 wrote:

> I have used both a Rolleidoscop and a Heidoscop
> camera.
>
> Both cameras utilized a red window which was about
> 3 inches in width.
>
> For reasons unknown to me, the cameras were not de-
> signed to be used with 120 film, and would only offer
> 5 stereo pairs per roll of 120 film.

I think these cameras pre-date the 6x6 markings on what we
now know as 120 film.

The instructions for my Rolleidoscop indicate it is made to
use "B2 6x9" film. And indeed, the window on the the back of
my 'scop lines up with the 6x9 markings on my 120 film which
accounts for it's odd advance sequence of lining up
different numbers at different places.

When used with a B2 "Six-spool", it would produce four
pairs. When used with a B2 "Eight-spool", it would produce
five pairs plus a half-pair.

> After removing the red celluloid window, I was able
> re-index the back of the cameras, allowing me to
> produce 6 stereo pairs on a roll of 120 film, which
> required a film advance that was accurate to within
> 1/16th of an inch. The numbers on the back of each
> roll of 120 film allowed this degree of accuracy.

While I understand that you are dead-set against the red
plastic in the window, Don, your same advance sequence can
be used with it in place. I used this advance sequence for
several rolls before I decided to narrow my film apertures
and eliminate my tendency to run off the front or back of
the film and overlap images.
http://stereo.thurstons.us/stock_advance.htm

I also thought about punching a new hole in the camera back
which would line up with the 6x6 markings on the paper. I
decided that was too much work and just made a new
paper-label to put under the existing door.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Subject: Re: getting this for the TL120
Date: 2008-07-16 07:41:01
From: dlopp2000

Based on the history, I believe that 120 roll film did have 6 x 6
markings, at the time my 1934 Heidoscop, and my 1937 Roleidoscop
were manufactured.

In 1934, the German), Eichapfel Noviflex reflex camera took
6 x 6 images, with the aid of a red window, on 120 film.

In 1935, the Reflex-Korelle SLR camera took 6 x 6 images on 120
film, with the aid of a red window.

In 1936, the Olympus Camera Co. of Japan produced a 6 x 6 folder
camera, the Semi-Olympus Model 1, which took 12 pictures on 120
roll film, with the aid of a red window.

The first Rollei, the Rolleiflex 1, a (6 x 6), camera did use a red
window to aid in advancing the 120 film properly. It was first pro-
duced in 1929.

My understanding is that the Rolleiflex, (6 x 6), TLR was designed,
by Franke & Heidecke, following the financial success of their roll
film stereo cameras.

I realize that German camera manufacturers, in the 1930's, were not
prone to make changes unless prodded by their competition. Franke &
Heidecke could have easily changed the position of the red window
in their stereo camera's, in the 1930's, to take advantage of the
6 x 6 markings on the available 120 film.

I can only guess as to why F & H did not alter their stereo cameras
to operate with the 6 x 6 marked 120 roll film.

The advertisements in the National Geographic magazine, (1938), cited
the soft shutter release on the Roleidoscop camera.

DON

friendly camera's in the 1950's.

A side point is that on all of the Heidoscop and Rolleidoscop
camera's that I have seen, contained Z Tessar lenses manufactured
in the year, 1927.

DON

Subject: A properly designed MF viewer.
Date: 2008-07-20 13:34:43
From: dlopp2000

I do consider MF stereo to be the optimum format for the viewing of
stereo images by individuals, when a user friendly viewer is used.

I do consider the Saturn MF viewer to be a satisfactory viewer for
those with, average eye spacing along with 20/20 vision, though its
optical distortion is a disappointment. I attribute the distortion
problem to the use of large diameter achromats.

I have mentioned that distortion can be a problem when a persons eye
spacing does not match the interocular spacing of the viewer lenses.

I do not believe that a 5 year old, (with an eye spacing of less
than 60mm), was able was able to make a valid determination that
little distortion was visible when viewing a MF slide in a Saturn viewer.
IMO, examples of, excellent, low distortion viewing lenses can be
found in the 3D world MF viewer, and in the MF viewer designed, and
built by Sam Smith. In both cases, the viewing lenses are not of
an excessively wide diameter.

My reason for having a controllable interocular, on my MF viewers
is not only for my benefit, but also, for the benefit of the other,
(approximately), 10 percent, who do not have an average inter-
ocular, of close to being about 65mm.

Also, for those that do not have 20/20 vision, I consider a user
friendly focus system should be available, as is the case with Sam
Smith's viewer.

I was recently asked whether or not I change the interocular on my
viewer. My answer was NO. The interocular spacing of my eyes,
(64.5mm), has not changed in the past 65+ years.

When I hand my viewer to someone else, and they show some viewing
discomfort, the problem is usually a focus problem, or an inter-
ocular problem. My viewers can be adjusted to fix both problems.

My eyes have a prismatic problem, which, in the past, has led me to
improperly position my slides. Sam Smith did show me how to prop-
erly position the viewer lenses, on my viewers, so that my viewers
would provide comfortable viewing for both myself and for those that
have normal vision.

DON

.

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 14:09:16
From: Michael Kersenbrock

dlopp2000 wrote:

> I do consider the Saturn MF viewer to be a satisfactory viewer for
> those with, average eye spacing along with 20/20 vision, though its
> optical distortion is a disappointment. I attribute the distortion
> problem to the use of large diameter achromats.
>

I believe the Saturn MF viewer had different
lenses included with it over time inasmuch I think they were "surplus"
lenses that were gotten on an as-available basis. That said, I think
they all were in the "large diameter achromat" category. Might the
different lenses have had noticeably different distortion characteristics?

Mike K.

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 18:19:08
From: dlopp2000

I agree that it is possible that some of the Saturn
were purchased as surplus achromats, but if my memory
is correct, their price was not the equal of what I
normally consider surplus lenses were priced.

I may be wrong, but I thought some of them came from
Edmund Scientifics, and they were not cheap.

The 78mm fl, 46mm diameter lenses are f/1.6 lenses.

I would not expect to see much quality in a two ele-
ment f/1.6 achromat.

The 75mm, f2.5 lenses in the 3D World viewers provide
a much higher degree of optical correction, at a sig-
nificantly lower cost. Their distortion level is very
low.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 21:48:59
From: Chuck Holzner

Don Lopp wrote:

> I do consider the Saturn MF viewer to be a

satisfactory viewer for

> those with, average eye spacing along with

20/20 vision, though its

> optical distortion is a disappointment. I

attribute the distortion

> problem to the use of large diameter achromats.

Given that you attribute the "distortion" to the
large diameter of the viewer's lenses, do you
think the "distortion" could be greatly reduced
by grinding the lenses to a smaller diameter?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 21:56:03
From: Chuck Holzner

Donald Lopp wrote:

> I do consider the Saturn MF viewer to be a

satisfactory viewer for

> those with, average eye spacing along with

20/20 vision, though its

> optical distortion is a disappointment. I

attribute the distortion

> problem to the use of large diameter achromats.

You never did mention the type of distortion you
found. Just what kind of distortion are you
talking about?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 22:09:55
From: Chuck Holzner

Donald Lopp wrote:

> I have mentioned that distortion can be a

problem when a persons eye

> spacing does not match the interocular spacing

of the viewer lenses.

> IMO, examples of, excellent, low distortion

viewing lenses can be

> found in the 3D world MF viewer, and in the MF

viewer designed, and

> built by Sam Smith.

All the 3D world MF viewers I have seen (the
cheap plastic ones) and all 3 of the Sam Smith MF
viewers I have seen (expensive but very nice) DO
NOT have adjustable Interoculars.
How then could they be distortion free? Please
explain.

Subject: Re: A properly designed MF viewer.
Date: 2008-07-20 23:55:10
From: dlopp2000

Yes, I do believe that, the distortion could be greatly reduced by
grinding a 30mm diameter lens, instead of grinding a 46mm diameter
lens, when the focal length of the lens is in the 75mm to 80mm range.

I have never seen a 40mm, or larger diameter achromatic lens that
did not have problems with distortion, (I am referring to achromats
that have a focal length of from 75 to 80mm). I previously compared
the visible distortion produced by the Saturns' 78mm fl lens, 46mm
diameter lens with the with the negligible distortion produced by
the 75mm fl, 30mm diameter lens on the World 3D MF viewer.

I am open to any examples that show me to be incorrect.

......................................................................

The distortion is of the pincushion type, which is easily seen, when
one views a MF slide.
........................................................................

I am not aware that there is a relationship between viewer lens
distortion and the presence or the lack of a presense of an
adjustable interocular.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 07:04:16
From: Brian Reynolds

Don wrote:

>
> I agree that it is possible that some of the Saturn
> were purchased as surplus achromats, but if my memory
> is correct, their price was not the equal of what I
> normally consider surplus lenses were priced.
>
> I may be wrong, but I thought some of them came from
> Edmund Scientifics, and they were not cheap.

If I recall correctly the first Saturn viewers used lenses from
Surplus Shed. I purchased a very early viewer kit without lenses as I
had already bought a set of surplus lenses (84mm focal length). When
the surplus supply dried up the various more expensive suppliers were
used.

--
Brian Reynolds | "It's just like flying a spaceship.
reynolds@panix.com | You push some buttons and see
http://www.panix.com/~reynolds/ | what happens." -- Zapp Brannigan
NAR# 54438 |

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 07:09:20
From: Chuck Holzner

Donald Lopp wrote:

I was recently asked whether or not I change the
interocular on my
viewer. My answer was NO. The interocular
spacing of my eyes,
(64.5mm), has not changed in the past 65+ years.

Am I to assume that you have the interocular on
your viewer set to 64.5 mm?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 09:16:25
From: dlopp2000

Regarding #, 1996.

You may assume what you wish to. as the lenses are set to the
position that offers the most comfortable viewing. I have not
bothered to measure what the position is, and I do not care what
it measures. My goal is comfortable viewing.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 09:36:14
From: dlopp2000

Regarding # 1995,

The 78mm fl, diameter 46mm were purchased from Edmund Scientific, as
part #, 42792, at a list price of, $120 each.

As I recall, the early Saturn lens spacing was changed to a different
and more user friendly lens spacing in the later models.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 16:30:48
From: dlopp2000

I was asked whether or not my viewer lenses had been set to being
spaced 64.5mm apart ?

My 80 year old eyes are not capable of noticing a quality difference
between a setting of 64mm and a setting of 65mm.

I consider the question to be pointless.

Red button viewers do have an adjustable interocular control.

I consider it unlikely that anyone ever sets the interocular spacing
to an accuracy of 1mm much less to an accuracy of .1mm on the red
button viewer.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 17:48:18
From: Chuck Holzner

Donald Lopp wrote:

> Yes, I do believe that, the distortion could be

greatly reduced by

> grinding a 30mm diameter lens, instead of

grinding a 46mm diameter

> lens, when the focal length of the lens is in

the 75mm to 80mm range.

Let me rephrase my question.

If you took the 46 mm lenses out of the Saturn
viewer and ground those lenses down to 30 mm
diameter and then remounted them in the Saturn
viewer (using bushings or a new lens board with
appropriate holes) would you no longer have the
objectionable pincushion distortion?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 19:05:54
From: Chuck Holzner

Donald Lopp wrote:

> I was asked whether or not my viewer lenses

had been set to being

> spaced 64.5mm apart ?

> My 80 year old eyes are not capable of noticing

a quality difference

> between a setting of 64mm and a setting of

65mm.

I thought that if you could measure the
interocular of the 3D World viewer, that you
could also measure the interocular of a Lopp
built viewer.

> I consider the question to be pointless.

The point of course is to figure out if you
adjusted the interocular of your viewer to your
eye spacing as you have previously suggested or
to some other parameter. You have said that you
do not adjust it to the infinity spacing on the
slides as you don't mount to a constant infinity
spacing and you never change your interocular for
your own viewing. I am just trying to figure
what you are doing and what infinity spacing
would give a parallel view to infinity in your
adjustable viewer that you do not adjust.
Apparently this number is not available.

> Red button viewers do have an adjustable

interocular control.

I know that, but the Red Button Viewer is not for
MF and won't view 80 X 132 slides, so it doesn't
really matter and should not be a subject on
MF3D.

> I consider it unlikely that anyone ever sets

the interocular spacing

> to an accuracy of 1mm much less to an accuracy

of .1mm on the red

> button viewer.

How would you know?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 19:15:48
From: dlopp2000

In the real world, ! am not aware that it is, mechanically possible,
to grind down a 46mm diameter achromatic lens into having a diameter
of 30mm.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 19:31:41
From: dlopp2000

According to #2001, the mounting of 35mm slides, and the adjustment
of the interocular of a 35mm viewer are based on a different principal
than is the mounting of MF slides. Also, the principal of the
interocular spacing of a medium format viewer, is also different than
it is with 35mm viewers.

I do not agree.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 19:31:41
From: dlopp2000

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 21:14:53
From: Chuck Holzner

Donald Lopp wrote:

> According to #2001, the mounting of 35mm

slides, and the adjustment

> of the interocular of a 35mm viewer are based

on a different principal

> than is the mounting of MF slides. Also, the

principal of the

> interocular spacing of a medium format viewer,

is also different than

> it is with 35mm viewers.

No one said the "principal" was different, Don.
The numbers are different and there is a lot of
"fixing problems where it is not broke" on
Realist format that we do not need on MF3D.
Realist format is better played on P3D or Film3D
and not on MF3D. Can we stick with MF stereo
here and not pollute it with Realist format
problems?

At present I am trying to figure why you have
alleged that a wider (46 mm) viewer lens in the
range of 75-80 mm will have too much Pincushion
Distortion but a narrower one (30 mm) will not.
I am NOT trying to change the subject.

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 21:14:53
From: Chuck Holzner

Donald Lopp wrote:

> In the real world, ! am not aware that it is,

mechanically possible,

> to grind down a 46mm diameter achromatic lens

into having a diameter

> of 30mm.

How about masking the 46 mm diameter lenses down
to about 30 mm so that the only part of the lens
that could be used was 30mm diameter. If that
was done, would it reduce the pincushion
distortion?

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-21 22:34:55
From: dlopp2000

Regarding #, 2006.

I can not think of any reason that the pincushion distortion problem
would be reduced by masking down down the 46mm diameter lens into
having a 30mm diameter.

The fact is, the 30mm diameter, World 3D MF viewer lenses do not have
a significant pincushion distortion problem, and the 46mm diameter
Saturn viewer lenses DO have a clearly visible pincushion distortion
problem.

I do not own a 46mm x 78mm fl lens, but YOU do own two of them lenses.

I suggest that YOU do the experiment, in real time.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 00:12:23
From: dlopp2000

Responding to # 2001.

I did not say that I adjust the interocular of my viewer lenses to
match my eye spacing.

I did say that I adjust the spacing of my viewer lenses so that they
do provide me a comfortable viewing experience.

I do not bother to measure the resulting interocular spacing, as I
am only interested in achieving a comfortable view, not in proving
an irrelevant theory.

My viewers do offer the option of matching the interocular spacing
of the viewer to that of the person involved.

The Saturn, and other fixed interocular viewers do not offer this
option, but mostof those with non-matching interocular eyeball
spacing do use these viewers, most without any complaints. An
adjustable interocular is useful for those that DO need the adjust-
ment option.

A question: Why should my viewer interocular be set to match the
interocular spacing of my eyes, while others do not have to match
their eyeball spacing to the interocular spacing of the various
fixed interocular viewers ?

I do not concur that the eyeball interocular should match the inter-
ocular spacing of the viewer lenses, which I believe, has been inferred.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 02:08:10
From: dlopp2000

The large diameter achromats, such as the 46mm diameter-78mm fl
achromats on the Saturn viewer, do have significant pincushion
distortion problems because they are not being used for what they
were designed for.were not designed to be used as viewer lenses in
a stereo slide viewer.

These lenses are industrial grade achromats which were designed to
be corrected for, "on-axis spherical and chromatic aberrations",
which is not appropriate for low distortion viewing of stereo slides.

I assume that World 3D did design their, (cost effective), 30mm
diameter achromats to produce negligible distortion, and they were
successful.

I believe that a mistake was made when the decision was made to use
large diameter viewing lenses for a MF viewer. For more than 8 years,
I have contended that smaller diameter, (less expensive), achromats
should be appropriate.

IMO, the excellent viewing optics in the MF viewer, made by Sam Smith,
validates my contention.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 07:12:23
From: Chuck Holzner

Donald Lopp wrote:

> A question: Why should my viewer interocular be

set to match the

> interocular spacing of my eyes, while others do

not have to match

> their eyeball spacing to the interocular

spacing of the various

> fixed interocular viewers ?

> I do not concur that the eyeball interocular

should match the inter-

> ocular spacing of the viewer lenses, which I

believe, has been inferred.

Not inferred at all; you should read more
carefully. It was you who said that the
interocular of a viewer should be adjusted
depending on the spacing of the person viewing's
eyes, not I. You said that the viewer
interocular was needed to match the different eye
spacing of different people. Not I.

I feel that the interocular of the viewer and
infinity spacing on the slide should be adjusted
to make the parallax depth cues match those of
viewing the real scene directly, which is best
done by matching the infinity spacing on the
slide to the interocular spacing of the viewer.
Matching the slide to the viewer interocular is
easily done if the viewer interocular doesn't get
moved around and you know what it is. The best
and cheapest way to keep the interocular from
being moved around is to make it fixed, as it is
in the 3D World (cheap plastic viewers) and in
all the MF viewers I have seen that Sam Smith
made as well as the Saturn.

It would be nice if all of the MF viewers had the
same interocular spacing.

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 08:15:45
From: Michael Kersenbrock

Chuck Holzner wrote:

> It would be nice if all of the MF viewers had the
> same interocular spacing.
>

Unless it also has very large lenses, such a viewer would be
unusable for my wife because she has serious problems with
35mm viewers with non-adjustable interocular spacing
inasmuch her eye spacing is wider than "normal".

A viewer with a fixed perfect view that's not see'able
isn't of great value.

Mike K.

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 10:17:58
From: Chuck Holzner

Donald Lopp wrote:

> The large diameter achromats, such as the 46mm

diameter-78mm fl

> achromats on the Saturn viewer, do have

significant pincushion

> distortion problems because they are not being

used for what they

> were designed for.were not designed to be used

as viewer lenses in

> a stereo slide viewer.

> These lenses are industrial grade achromats

which were designed to

> be corrected for, "on-axis spherical and

chromatic aberrations",

> which is not appropriate for low distortion

viewing of stereo slides.

Sounds like Don has changed his tune.

Whatever the reason that the 46mm diameter -78 mm
fl achromats on the Saturn viewer "have
significant pincushion distortion", it is not
because they are too wide.

I have made a donut hole shaped cardboard
aperture 46mm wide with a 3/4" hole (19 mm,
closest to 30mm hole punch I have) in the center
and placed it over one of the lenses. Looking at
a slide with it, there is no change in pincushion
with or without the aperture in place. My
conclusion is that whatever causes pincushion,
lens diameter is not it.

> I assume that World 3D did design their, (cost

effective), 30mm

> diameter achromats to produce negligible

distortion, and they were

> successful.

I read somewhere that they bought the lenses but
don't remember where, likely I read it on one of
these groups. I have also read, on one of these
groups, that they are discontinuing the cheap
plastic viewer and the replacement viewer will
have different lenses. Doesn't sound all that
successful to me.

> I believe that a mistake was made when the

decision was made to use

> large diameter viewing lenses for a MF viewer.

For more than 8 years,

> I have contended that smaller diameter, (less

expensive), achromats

> should be appropriate.

For 8 years you have been complaining about a
viewer you do not even own? Are you now saying
that "pincushion" is a trade off with "on-axis
spherical and chromatic aberrations"? Trade one
distortion for another?

The wider lenses are there to make the viewer
work with a wider range of eye spacing.

My suggestion to you is to get a Saturn with a
board to take the 30 mm wide lenses spaced 65 mm
apart and break apart one of the cheap plastic
viewers for the lenses and insert them in the
Saturn. Or better yet put the 30 mm lenses in
one of your own handmade viewers.

%^)

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 10:23:49
From: Chuck Holzner

Michael Kersenbrock" wrote:

> Unless it also has very large lenses, such a

viewer would be

> unusable for my wife because she has serious

problems with

> 35mm viewers with non-adjustable interocular

spacing

> inasmuch her eye spacing is wider than

"normal".

>
> A viewer with a fixed perfect view that's not

see'able

> isn't of great value.
>

Yes Mike, That is why the Saturn has the wide
lenses.

Chuck Holzner

Subject: observing distortion in viewer lenses [was: A properly designed MF
Date: 2008-07-22 11:17:40
From: John Thurston

Chuck Holzner wrote:

> I have made a donut hole shaped cardboard aperture 46mm
> wide with a 3/4" hole (19 mm, closest to 30mm hole punch
> I have) in the center and placed it over one of the
> lenses [of the large diameter lens in the Saturn viewer].
> Looking at a slide with it, there is no change in
> pincushion with or without the aperture in place. My
> conclusion is that whatever causes pincushion, lens
> diameter is not it.

Chuck, I think a better test would be to take that mask you
made and shift it off-center and see how the image appears
that way. This would better simulate the view a narrow-eyed
person would see through the lenses.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 12:22:57
From: dlopp2000

I shall attempt to clarify my stand on large
diameter achromats versus small diameter
achromats, to counteract distortions of my
allegations.

IMO, optical quality, (assuming good qual-
ity control), is determined by what the
achromats were designed to be used for,
not by their diameter, whether large or
small.

All of the achromats that I have installed
in my MF viewers were designed for photo-
graphic use, or came from World 3D viewers.

As best I can tell, all of the commercially
available achromats that I am aware of,
(often as surplus optics), are usually in-
dustrial achromats, and were not designed
to be used in stereo slide viewers.

Control of distortion problems was not taken
into account when the industrial achromats
were designed.

DON

Large diameter achromats can be designed that
do not produce significant pincushion distor-
tion.

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 12:36:40
From: dlopp2000

Regarding # 2011.

Hopefully, in the near future, I will be able
to test an adjustable interocular MF viewer
with Mike K, and his wife.

She has already tried a Saturn viewer, and it
failed to be usable, with her 70mm interocular.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-22 13:03:44
From: dlopp2000

Regarding 2012.

I only started complaining about the large
diameter lenses on the Saturn MF viewer
after using a Saturn about 8 years ago.

A few years ago I did see significant
distortion in your Saturn viewer.

I have NO intention of wasting my money on
a Saturn viewer.

"On axis spherical aberrations", are not a
distortion problem, as has been alleged.

DON

Subject: Re: observing distortion in viewer lenses [was: A properly designed
Date: 2008-07-22 13:35:05
From: Chuck Holzner

"John Thurston" Wrote:

> Chuck, I think a better test would be to take

that mask you

> made and shift it off-center and see how the

image appears

> that way. This would better simulate the view a

narrow-eyed

> person would see through the lenses.

I was afraid that one test would lead to another.
%^)

Moving the mask to the side eventually gets me to
where I can not see all the way to a side
anymore. Sharpness degrades some too. The
"pincushion" doesn't change at all up until the
edge gets blanked out.

For another test, I broke out some of my 35mm
viewers and found "pincushion" in all of them,
some more than others. My Kodaslide II, TDC and
my 6X from John Golden all have "pincushion
distortion". I don't have a Red Button to test.
It seems that the more magnification the viewer
has the more "pincushion" it has. I guess that
none of my viewers are using lenses that were
designed for viewers.
%^)

It is interesting that I never really saw the
"pincushion" in my Saturn until Don mentioned it.
It never jumped out to me, and seems to be so
little that I wonder why anyone would care. I
can't use a Cheap China Viewer because I can't
focus them, so I can't compare them to the
Saturn.

BTW, How are you coming with your 50 mm FL MF
viewer. I would love to see it working with your
wide angle slides. Virginia is a long way from
Alaska. Maybe next NSA.

Cheers,

Chuck Holzner

Subject: Re: observing distortion in viewer lenses [was: A properly designed
Date: 2008-07-22 13:49:06
From: roderickdsage

Yea, I wasn't aware of pincushion in the Saturn viewer either. Now I
will always be aware of it. It doesn't bother my though. I think the
optics are great. I am more disturbed by chromatic aberration and I
see none in these lenses. I know that later Saturn viewers used
different lenses. I have an early one. I don't have a 3D-World
viewer and can't compare.

Rod S

--- In MF3D-group@yahoogroups.com, "Chuck Holzner" <3D4me@...> wrote:
>
snip
> It is interesting that I never really saw the
> "pincushion" in my Saturn until Don mentioned it.
> It never jumped out to me, and seems to be so
> little that I wonder why anyone would care. I
> can't use a Cheap China Viewer because I can't
> focus them, so I can't compare them to the
> Saturn.
>

Subject: Re: observing distortion in viewer lenses [was: A properly designed
Date: 2008-07-22 13:54:31
From: John Hart

--- In MF3D-group@yahoogroups.com, "Chuck Holzner" <3D4me@...> wrote:

> BTW, How are you coming with your 50 mm FL MF
> viewer. I would love to see it working with your
> wide angle slides. Virginia is a long way from
> Alaska. Maybe next NSA.

Mesa AZ is a long way from both places, eh? Be nice if more MF'rs
showed up though. At GRap there was a small meeting (w/ about 20
enthusiasts) hosted by Dave Kesner. Dale Yingst brought a saturn
viewer equipped with 58mm lenses (or was it 55's?). John Thurston's WA
test slides, from a folio Dave had, looked pretty good, though there
was a fair amount of vignetting at the corners. I'm still waiting for
the 3Dworld focussing viewer, because I can't focus the current one
either, and if I use diopters I get lots of vignetting there too. Dr.T
says "no word" on these new viewers, but he volunteered to check
again. Maybe in time for all those MF shots of the Olympics ;-)?

John

Subject: Re: observing distortion in viewer lenses
Date: 2008-07-22 16:51:45
From: John Thurston

Chuck Holzner wrote:

> BTW, How are you coming with your 50 mm FL MF viewer. I
> would love to see it working with your wide angle slides.
>

So would I! Unfortunately, I haven't been able to devote
much time to it :( Fortunately, the things that have been
getting in the way have been things like riding bikes,
hiking in the mountains and time with my children :)

I have a backpacking trip next week, a week home, then a
week at my son's soccer tournament. After _that_ Juneau
should be well into the fall rains and maybe I'll have time
to attack that viewer design again. I'll let 'cha know when
I've made some progress.

> Virginia is a long way from Alaska. Maybe next NSA.

Living in Alaska for the past seventeen years has affected
my ability to enjoy warm weather, so I'm a little concerned
with a convention in Mesa. _But_, I'm still thinking I
should try to attend the 2009 convention. Phoenix is a
direct Alaska Air flight from Seattle so it's only 2,000
miles/seven hours from here. If I plan ahead, I may be able
to do it on miles which will reduce the cost some :)
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Subject: Re: observing distortion in viewer lenses [was: A properly designed
Date: 2008-07-22 21:40:17
From: dlopp2000

Regarding # 2022

I saw my first saturn viewer several years
after I made my first MF viewer, which had
rack and pinion focus, plus an adjustable
interocular.

My initial impression was that it was a bit
primitive.

As time went by, I assumed that an improved
model, (such as rack and pinion focus),
would be offered, but it never happened.

The on line discussion included a discussion
of the, so called, advantages of mounting
the slides to a set infinity position, which
would match the interocular spacing of the
viewer lenses.

At the time, I was mounting my slides to the
window. I am still mounting them to the
window.

I do not understand the reason as to why I
should have changed my mounting strategy.

As long as I restrict my, "Maximum On Film
Deviation", (MAOFD) to be less than 2.0mm,
my slides will never require that I diverge
my eyeballs.

Of the hundreds of MF slides that I have seen
in recent years, almost all of them have been
mounted to the window.

Are most of us doing it the wrong way ?

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-23 18:24:03
From: dlopp2000

I am curious as to how a person, (PT), with an eyeball spacing of
58mm will be able to view a MF slide, (when the slide is mounted with
the infinity points spaced 62 mm apart), without running into the
problem of being forced to diverge eyeballs, when the viewer is a
Saturn which has a fixed interocular ?

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-23 19:03:41
From: Chuck Holzner

Donald Lopp wrote:

>I am curious as to how a person, (PT), with an

eyeball spacing of

>58mm will be able to view a MF slide, (when the

slide is mounted with

>the infinity points spaced 62 mm apart), without

running into the

> problem of being forced to diverge eyeballs,

when the viewer is a

> Saturn which has a fixed interocular ?

Given your numbers above and assuming the Saturn
has an interocular of 65.5mm as does mine, he
would have to converge his eyes to view infinity.
And all the depth in the slide will be in front
of the window if he is using one of the
commercial mounts. (likely lots of WVs.)

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-23 22:18:13
From: LeRoy Barco

Re: [MF3D-group] Re: A properly designed MF viewer. The prismatic effect of looking through the inner edges of the lens makes it work.

Similar to the Holmes/Bates stereoscope for viewing classic stereoviews. The “lenses” of the stereoscope are actually cut out of the edges of large lenses which would have their centers spaced at about 3 1/2 inches which is typical infinity spacing of the 3 inch images on a classic view.

Of course, one then accepts whatever distortion comes from looking through the centers of the lenses. And the lenses have to be large enough to work with other than “normal” eye spacing.

LeRoy

On 7/23/08 6:23 PM, "dlopp2000" wrote:

I am curious as to how a person, (PT), with an eyeball spacing of
58mm will be able to view a MF slide, (when the slide is mounted with
the infinity points spaced 62 mm apart), without running into the
problem of being forced to diverge eyeballs, when the viewer is a
Saturn which has a fixed interocular ?

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-24 00:53:16
From: dlopp2000

Regarding the possibility of a quality view by people with a narrow,
58mm interocular.

I disagree, as this through the edge/prism effect only works with
low magnification optics, which is the case with the Holmes viewer.

In the case the of the Saturn 78/46mm lenses it does not apply.

As one looks through the lens, off axis, one brings on aberrations,
such as keystone distortion.

If one will position their eyeball about 4mm (3/16") off center, the
"keystone effect", can be seen, as it would be seen by a person with
a 58mm interocular, when the viewer lenses are spaced 65.5mm apart.

As I said before, Sam Smith and World 3D have shown us that higher
quality viewers optics are possible.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-24 21:01:28
From: roderickdsage

--- In MF3D-group@yahoogroups.com, "dlopp2000" wrote:

>
> Regarding the possibility of a quality view by people with a narrow,
> 58mm interocular.
>

SNiP.

>
> DON
>

I guess those poor soles are just SOL!

RS

Subject: Re: A properly designed MF viewer.
Date: 2008-07-24 21:11:44
From: Chuck Holzner

Donald Lopp wrote:

> I disagree, as this through the edge/prism

effect only works with

> low magnification optics, which is the case

with the Holmes viewer.

> In the case the of the Saturn 78/46mm lenses it

does not apply.

I am sorry Don, I must have missed it. What is
the shortest FL where this law of optics does
apply?

Thanks,

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-24 21:17:59
From: dlopp2000

No, those with an IPD of 58mm are only out of luck if they are
restricted to using a Saturn viewer. In my viewers they would
not have this problem.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-24 21:35:56
From: Sam Smith

OK, I'm probably going to regret it but I'll add my two cents. Your
both right in my opinion. Yes, there is a prismatic effect at the edge
of all viewing optics. But I think you may have missed what I
perceive to be Don's point, that it doesn't "work" the same at all
focal lengths. I interpret this to meaning it does not give an
effective working stereo image. The key issue is what is known as the
"sweet spot" in viewing lenses. This is roughly defined as the area
around the central axis of the optic that is free of perceptible
distortion when looking through it. Long focal length lenses like
those in a Holmes viewer have very large sweet spots, however those in
a typical MF3D viewer do not. I can't recall that precise amount, but
I believe I figured it to be around 10mm for a typical achromat on the
75-85mm range. Viewing outside this spot will yield a perceptible
amount of loss of sharpness and other distortions. Increasing the
diameter of the lens adds nothing, in fact gives less. Although you
may see more in a larger optic and feel that there is more light
bending properties to correct the differences in eye distance between
different users, the tradeoff is more distortions. The use of an
interocular adjustment makes it possible for those with either farther
or closer eye spacing than normal to adjust the viewer and obtain as
much viewing through the sweet spot as possible.

I had search for a lens for years that had a larger sweet spot than
the 10-15mm range and never found one that was suitable for viewing.
Correcting this distortion always meant more elements, and more
elements meant vignetting from the barrel edges. As for shorter
optics, the sweet spot grew even smaller, requiring even more
necessity for interocular adjustment.

Hopefully I haven't confused the issue.

Sam

--- In MF3D-group@yahoogroups.com, "Chuck Holzner" <3D4me@...> wrote:
>
> Donald Lopp wrote:
>
> > I disagree, as this through the edge/prism
> effect only works with
> > low magnification optics, which is the case
> with the Holmes viewer.
>
> > In the case the of the Saturn 78/46mm lenses it
> does not apply.
>
> I am sorry Don, I must have missed it. What is
> the shortest FL where this law of optics does
> apply?
>
> Thanks,
>
> Chuck Holzner
>

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 00:35:59
From: dlopp2000

I recently suggested that the 78/46mm
viewer lenses on the Saturn viewer.
I based my allegation on the fact that
these lenses are about 18mm thick in
the center.

The 75/30mm viewer lenses on the world
3D viewer are only about 10mm thick,
have a larger sweet spot, and produce,
significantly, less distortion problems.

A much thinner lens, the, "pinhole lens'
is very thin, and produces almost zero
distortion

It was recently suggested that distortion
problems might be reduced by masking down
a lens, but stopping down a lens does not
alleviate potential distortion problems.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 01:02:26
From: dlopp2000

As regards to # 2033.

I was referring to the lenses used in viewers.

That should indicate the potential focal lengths that are involved.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 15:58:03
From: Chuck Holzner

"Sam Smith" wrote:

> The key issue is what is known as the
>"sweet spot" in viewing lenses. This is roughly

defined as the area

>around the central axis of the optic that is

free of perceptible

>distortion when looking through it. Long focal

length lenses like

>those in a Holmes viewer have very large sweet

spots, however those in

>a typical MF3D viewer do not. I can't recall

that precise amount, but

>I believe I figured it to be around 10mm for a

typical achromat on the

>75-85mm range.

Okay, So "Sweet Spot" is the size of the
"usable" diameter of the viewer lens. We are
starting to make some sense now. The "sweet
Spot" is independent of lens diameter meaning
that larger lenses may not have a larger "Sweet
Spot" than a smaller lens but it could.
Obviously it is the largest "useable diameter"
that we would use to cover the widest range of
eye spacing.

With a viewer Interocular of 65 mm and a "Sweet
Spot" of 10 mm that would seem to work with a
range of 55 to 75 mm eye spacing. If we subtract
a pupil diameter of 4 mm from the "Sweet Spot"
we will still accommodate eye spacing from 59 to
71mm. That works out to 98% of adults. No
wonder a large % of people seem to have no
problem viewing with a Saturn.

That Said, I will say that a viewer manufacturer
should go with the lenses with the widest "Sweet
Spot", especially if they are otherwise sharp,
distortion free, proper FL, and cheap.

It would appear that both the Cheap Plastic China
Viewer and the Saturn are now out of production.
3D-World is supposedly working on a new viewer
but doesn't have one yet. Most likely it will
work with their Plastic 80X140 mounts and only
with the "pre-3D-World" standard 80X132 mounts by
using an adaptor of some sort. I have not heard
that Sam Smith has gone into mass production of
his viewers but no doubt I will be corrected if
that is in error.

Somehow I get the feeling that this whole thread
has been a "fishing trip" to "test the waters" to
see if the market is right for a new viewer and
to find out just what people will want. We
already know what Don Lopp would want and we know
he has been plugging Sam Smith's viewer quite a
bit lately.

Here is what I would want should I be looking
to buy an new viewer:

1) 75mm FL lenses (to match the Sputnik FL).

2) Wide user range (Sweet Spot). Actually I
don't need that with my middle of the range 65 mm
eye spacing but it would sell better that way. I
want great resolution as prime quality, "Sweet
Spot" comes in second.

3) A focus adjustment that is quick and easy but
will stay where I put it until I want it changed.
(I don't change focus much unless I am passing
the viewer around.)

4) A fixed interocular of 65 MM, as in all the
Sam Smith viewers I have seen, Both of them. (My
favorite infinity spacing for MF as well as the
middle of the eye spacing range.) Also helps
keep the cost down. Adjusting the interocular
not only moves the "Sweet Spots" but, at the same
time, moves the parallax, the main source of
stereo vision, and a depth cue I want in
alignment with all the other depth cues. If I
have to live with an adjustable IO I would want
it either with detent stops clearly marked as to
the IO or a micro dial that is calibrated for it.
I want to be able to set it without a lot of
testing/measurement and leave it there.

5) Will work easily with both the 80x132 and the
80x140 mounts interchangeably.

6) A good white, very evenly distributed, back
light. Batteries that charge and can be used
when the viewer is plugged into AC power.

The Proto-type Sam Smith Viewer that I saw a year
ago had at least most of these features, as I
recall.

Other plus items could be:

Easily adapted to shorter FL lenses for viewing
with lenses in the range of 50-60 mm FL.

Ability to properly view glass mounted slides ( I
know of only one stereographer now using them.)
that always seem to be extra thick and have the
chips mounted rather far apart. (Only real need
for an adjustable interocular. AFAIK)

Thanks for reading,

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 18:14:40
From: Sam Smith

--- In MF3D-group@yahoogroups.com, "Chuck Holzner" <3D4me@...> wrote:

> With a viewer Interocular of 65 mm and a "Sweet
> Spot" of 10 mm that would seem to work with a
> range of 55 to 75 mm eye spacing. If we subtract
> a pupil diameter of 4 mm from the "Sweet Spot"
> we will still accommodate eye spacing from 59 to
> 71mm. That works out to 98% of adults. No
> wonder a large % of people seem to have no
> problem viewing with a Saturn.
>

I totally disagree with this assessment. It does not take into account
two key variables:

1. The surface of the pupil is not directly on the surface of the
viewing lens, but at least 5mm from it.

2. It does not take into account that the eyes are pivoting as they
view details of the image including the extreme corners. That means if
you have the "ideal" interocular and were looking at the edges of a
stereo image, the pivot point of your eye is possibly 15mm from the
lens. I'm sure someone can work this out on Cadd, but my guess that a
30 degree pivot under "ideal" conditions would lead to nothing at all
as far as accommodation. Only an interocular could offer some
correction for this. I will commit 3-D blasphemy by saying that
neither McKay or Ferwerda ever acknowledged this, and every line
drawing I've ever seen was showing the eye only looking at the center
of the image. If only the center of the stereo image was important
than I guess I'm going to have to make a radical change in my
compositions.

>
> Somehow I get the feeling that this whole thread
> has been a "fishing trip" to "test the waters" to
> see if the market is right for a new viewer and
> to find out just what people will want. We
> already know what Don Lopp would want and we know
> he has been plugging Sam Smith's viewer quite a
> bit lately.
>

I think that feeling may have been brought on by something you're
smoking (and not passing around to the rest of us)!!! I have no
interest in making any more viewers, and am not part of any offlist
discussions of the topic. I would however be more than happy to share
with others what I have learned. I as only interested in clearing up a
few misconceptions.

Sam Smith

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 19:04:57
From: dlopp2000

Regarding # 2043.

An amazing wish list was presented.

Such as: The viewer lenses being sharp, dis-
tortion free, have a wide sweet spot, and be
cheap.

If, "cheap", is possible, what a bargain.

I believe that Sam Smith mis-spoke when he
described the sweet spot as being an area
that is free of perceptible distortion when
looking through it. All of the achromats
that I have seen, to date, present a visible
distortion problem.

My idea of a sweet spot is the central lens
area that permits a sharp view of the entire
image of the film chip, with or without vis-
ible distortion.

My best achromatic viewer lenses contain vis-
ible distortion though much less than what is
seen in the the widely used,Saturn 78/46mm
lenses.

When Holmes viewer lenses are being used,
the view is seen through the off center part
of the, (1/2 section of the lens), so as to
take advantage of the prism principal to per-
mit the viewing of stereo cards, which have
their images spaced more than 75mm apart.

I am satisfied with my latest MF viewer which
does offer rack and pinion focus, accommodates
lenses with focal lengths of 55mm and longer,
offers an IPD range of from 60 to 75mm, uses
a 5000K panel light, and does accept both the
132mm and 140mm wide slide mounts.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 20:01:20
From: Sam Smith

Be patient Don, you posted this 6 times!!!! I deleted the other copies.

Sam

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 20:14:17
From: Chuck Holzner

"Sam Smith" wrote:

> 1. The surface of the pupil is not directly on

the surface of the

> viewing lens, but at least 5mm from it.

With the eyes and viewer focused for infinity,
The light rays coming to the eye from the focal
point will be parallel and so the area will stay
the same no matter how far from the lens the eyes
are located.

>2. It does not take into account that the eyes

are pivoting as they

>view details of the image including the extreme

corners. That means if

>you have the "ideal" interocular and were

looking at the edges of a

>stereo image, the pivot point of your eye is

possibly 15mm from the

>lens. I'm sure someone can work this out on

Cadd, but my guess that a

>30 degree pivot under "ideal" conditions would

lead to nothing at all

>as far as accommodation.

So you did not consider that in the "calculation"
of "Sweet Spot". I have never seen the term
"Sweet Spot" in any text book on lenses so can't
comment on it's definition.

> Only an interocular could offer some
> correction for this. I will commit 3-D

blasphemy by saying that

> neither McKay or Ferwerda ever acknowledged

this, and every line

> drawing I've ever seen was showing the eye only

looking at the center

> of the image. If only the center of the stereo

image was important

> than I guess I'm going to have to make a

radical change in my

> compositions.

So we are in a magic land where no one knows what
is really happening. As I noted before, you
can't adjust out any distortion with the
interocular without screwing up the parallax.

> I think that feeling may have been brought on

by something you're

> smoking (and not passing around to the rest of

us)!!!

Actually it was Don's repeated praise of your
viewer and his consistent downing of the Saturn
and their lenses that was most of the smoke
passed around.

>I have no
>interest in making any more viewers, and am not

part of any offlist

>discussions of the topic. I would however be

more than happy to share

>with others what I have learned. I as only

interested in clearing up a

>few misconceptions.

I guess we (I) need a good definition of what a
"Sweet Spot" really is.

So I will stick with my Saturn until something
better comes along.

Chuck Holzner

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 20:26:16
From: Chuck Holzner

----- Original Message -----
From: "Sam Smith" <groups@stereoscopia.com>
To: <MF3D-group@yahoogroups.com>
Sent: Friday, July 25, 2008 10:01 PM
Subject: [MF3D-group] Re: A properly designed MF
viewer.

Be patient Don, you posted this 6 times!!!! I
deleted the other copies.

Sam

I counted 9. A real smoke screen.

Enough of this,

Chuck

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 20:26:42
From: dlopp2000

Regarding # 2043.

An amazing wish list has been presented:

The lenses being sharp.

The lenses being distortion free.

The lenses being cheap.

A real possibility ?

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 21:11:25
From: dlopp2000

Regarding # 2056, I believe that those that use the words, "sweet
spot", should offer their definition of the words.

My definition is:

The central portion of an achromat lens that permits
a sharp view of the entire area of the film chips.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-25 21:33:38
From: dlopp2000

Regarding # 2055, I do not believe that the light rays
are parallel when they come from the corners of the
film chip,

I am not aware that the human eye is able to see both
the center image and the corner image, of a film chip,
at the same time. The eyeballs must rotate to see
the corner images.

DON

Subject: My Dream MF viewerwit pix.
Date: 2008-07-26 10:32:24
From: dlopp2000

I recently read that someone wants to
have a MF viewer, which has a FOV ep
of only about 80 degrees.

Not a problem, if one can find a 35mm
focal length viewer lens.

Would such a MF viewer be of any use, for
those that do not have 35mm fl taking
lenses ?

Would such a lens, (35mm fl) allow an in-
terocular spacing to be as narrow as 65mm ?

Would this WA viewer be suitable for those
that have an IPD of 60mm, or less.

Would this 35mm, (WA lens), produce a low
distortion image ?

What value would such a viewer have for we
stereo addicts ?

DON

Subject: Re: My Dream MF viewerwit pix.
Date: 2008-07-26 11:02:16
From: Bill G

Hi Don

> I recently read that someone wants to have a MF viewer, which has a FOV ep of only about 80 degrees. Not a problem, if one can find a 35mm focal length viewer lens.
>

If a 35mm viewer fl ever existed that produces
an 80 deg AFOV, than PLEASE advise me where it's at!!!! Using a
typical 29mm horizontal width of the film as an example..... if there
was a 35mm viewer lens with a 29mm fl, it would produce a 53 deg. AFOV
(leaving distortion out of the equation).

(when linear film dimension equals fl, AFOV always equals 53 deg.)

However, I have never seen a 29mm fl lens used in a 35mm viewer.
The lowest fl's I have been aware of, is in the 45mm fl range,
producing a 35 deg. AFOV....which is still impressive, as it matches the
AFOV of the 3d world MF viewers 75mm fl lenses with 52mm sq. film.
However 53 degrees, in optics terms, is miles from the 80 degrees AFOV
you suggest. The difference when looking at an 80 degree AFOV vs. a 35
degree AFOV EP is staggering.... as it projects an image with 5x the
area onto the retina....the gains are not linear, which is why it's so
desirable.....but yet, so difficult design, and expensive to prototype
and build.

> Would such a MF viewer be of any use, for those that do not have 35mm fl taking lenses ?
>

Taking lenses and viewing lenses do not have
to be the same fl. In theory, there is some expansion / contraction on
the Zaxis when using mis matched viewing and taking fl's. But I have
experimented extensively with this, and this is one area where our brain
is very forgiving. In MF, I have 35mm fl shots viewed in 80mm fl
viewer lens and the view is spectacular.... also in MF, I have seen
44mm fl viewing lenses with 120mm taking lenses, and once again, the
views are spectacular..... Thankfully, our brains through us a bone in
this area, opening up more possibilities. This is one of the few
"forgiving" areas our brain allows with no mental stress penalties.
The only caveat is, no extreme close ups.... from ~8ft out, everything
looks natural.

> Would this WA viewer be suitable for those that have an IPD of 60mm, or less. Would this 35mm, (WA lens), produce a low distortion image ?
>

With the right design, it can be made with
near ZERO distortion (<.5%) , and offer IPD range of 55mm to 85mm.

> What value would such a viewer have for we stereo addicts ?
>

Therein lies the biggest problem IMO....
the market is so small for these products, it seems senseless to dump
the R&D, prototyping cost, manufacturing runs, etc into a viewer that so
few would ever sell..... 1950's is long over....

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-26 14:35:55
From: dlopp2000

I am curious as to how or why the World 3D MF viewer
qualifies such that it can be described as being a,
"Cheap", MF viewer.

I consider it to be a bargain, the optics are
great, and the construction is very robust.

I consider its focus problem as being fixable.

Especially if the viewer is not to be used by the
near sighted.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-26 14:53:43
From: Aaron Muderick

I would love to use this viewer without my glasses. I can live with my astigmatism. However, I need far-sightedness corrected to make anything of the image. I'd prefer hacking a $30 viewer than building my own Saturn for $150+.

I am new to this sort of thing but I'm a quick study. Thanks!

Aaron

dlopp2000 wrote:

I am curious as to how or why the World 3D MF viewer
qualifies such that it can be described as being a,
"Cheap", MF viewer.

I consider it to be a bargain, the optics are
great, and the construction is very robust.

I consider its focus problem as being fixable.

Especially if the viewer is not to be used by the
near sighted.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-26 16:43:58
From: Bill G

> I am curious as to how or why the World 3D MF viewer
> qualifies such that it can be described as being a,
> "Cheap", MF viewer.
>

I concur here..... But more significantly,
I think the 3d world "mounting jig" is the best value MF viewer ever
produced. It provides focus, great back light and sells for < $200
from Dr. T. No production viewer will ever match its price /
performance ratio.

Yes, its not designed as a viewer, but it can be hacked to become
one. Of course, the limitation is the optics.... it's designed for
those with very close to 64mm IPD, and who do NOT have astigmatisms or
mis matched refractive errors in their eyes, cause the damn ER is so
short, it can NOT accommodate EG wearers without significant vignetting
and image clipping. So, it does have limitations, but if you fall
within its limitations, it's a superb viewer considering the low
price. I have no inside knowledge, but I see no reason why 3d World
won't take this mounting jig design to the next level and make a
focusable back lit viewer.... This hobby really needs that viewer, so
write your to your Senators! :-)

Or in our case, Dr. T, as he speaks Chinese.... ;-) or better said,
they communicate with him.

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-27 01:28:08
From: Bob Aldridge

My 3D World mounting jig (that I got as part of the camera kit in April) came with a slide holder to turn it into a slide viewer. Only works with their mounts, of course, but it really is a great slide viewer.

Bob Aldridge

From: MF3D-group@yahoogroups.com [mailto:MF3D-group@yahoogroups.com] On Behalf Of Bill G
Sent: 26 July 2008 23:44
To: MF3D-group@yahoogroups.com
Subject: Re: [MF3D-group] Re: A properly designed MF viewer.

> I am curious as to how or why the World 3D MF viewer
>

qualifies such that it can be described as being a,

> "Cheap", MF

viewer.

>

Subject: Re: A properly designed MF viewer.
Date: 2008-07-27 22:01:33
From: dlopp2000

I recently read that MF transparency films had a resolution max
of about 30 lp/mm. (My interpretation may be in error.) In real
life, Velvia 50, is capable of resolving at least 56 lp/mm, which can
not be seen in my MF viewer when my viewer has its 68mm, (3.7x), fl
lenses. 56 lp/mm is too fine to be seen, even, in a red dot viewer
which has a magnification factor of about 5.8X.

I do consider the limitting factor in the resolution capabilities
of MF slides, is the currently available, low resolution color films.
Sam Smith has sent, around a few of his B & w MF slides. These
slides, probably, had resolution as high as 100 lp/mm.

A few years ago I sent a film sample with this degree of reso-
lution S. who could see this degree of resolution, to Boris S.,
who said that he could see 56 lp/mm. I argued with Boris that
I didn't believe 56 lp/mm res was possible, but I forgot that he
was using a differen standard than I was, as Boris was reading
the radial resolution, whereas I was thinking in terms of lens
resolution, where the resolution must include both the radial and
the tangential, not just the radial. I was wrong, and Boris was
correct.

I am curious about the 60mm fl lens that had a diameter of 4 inches,
(102mm). Is this a f/0.6 , 'dream', lens ?

Also, I don't believe that it a fact that most viewers have a, "very
low light level".

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-27 23:48:05
From: Bill G

Hi Don

> 56 lp/mm is too fine to be seen, even, in a red dot viewer which has a magnification factor of about 5.8X.
>

There is two interesting topics regarding seeing detail.... one is
resolution as you suggest, and the other is our ability to "discern"
differences in resolution, above what we can resolve. If you want an
interesting book that discusses how much resolution humans can "discern"
that relates to photographic images (i.e. differentiate from lower
rez, to higher rez images above our capacity to truly resolve), then I
suggest reading Cteins first book called POST EXPOSURE. In summary, he
had a very eloquent test system whereas subjects could properly place
the same image printed at different resolutions in proper order, from 5
lp/mm to 50 lp/mm, in 5 lp/mm increments. A very high % of the test
subjects (90%+ IIRC) placed the 6 images from 5 - 30 lp/mm in proper
order....from 30 lp/mm and higher, the subjects could not place them in
proper order. This gives an idea of how much resolution capacity human
vision has.

Of course, this test was done with unaided vision, at normal viewing
distance. (unless the subjects needed to wear their corrective eye
wear) Viewing distance is a critical factor in any resolution test,
as you half the view distance, you can resolve 2x more resolution.
Assuming the avg. view distance in this test was 16", and you want to
draw a parallels to stereo viewing, where we view at 2", (for 50mm fl)
our ability to "discern" would be closer to 180 lp/mm (8 x 30). Far
more than any film could ever hold. DISCERN, NOT RESOLVE!

As for resolution, it's widely accepted the avg. healthy eye human can
resolve about 3 lp/mm. Of course there is a wide range here, Top Gun
fighter pilots often can resolve up to 7 - 10 lp/mm, whereas older
people with even slight retinal degradation often can only resolve 1 - 2
lp/mm. Anyway, using the conventional standard of 3 lp/mm, with an
avg view distance of 16" (subjective), that same person at 2" (50mm
optic) could resolve up to 3 x 8 = 24 lp/mm. Considering avg. losses
of ~ 50% from the viewer optics and eye aberrations, specially with a
5mm pupil diam., the on-film resolution would need to be 2x greater to
deliver 24 lp/mm to the retina, or 48 lp/mm. This is about the avg.
max. color chrome film can hold, considering you are not shooting wide
open, using flat subjects. This is why a 40 - 50mm fl MF viewer is the
true sweet spot for human vision, assuming the optic is near diffraction
limited. (lots of issues in the capture process, such as film type,
lens MTF, film flatness, f stop, shutter speed, etc.)

As a reality check, you can reverse the process and start from the
retina and move to the film. At the fovea, the max resolution
possible, based on the size of our fovial cones, is 140 lp/mm.
(Ironically about equal to a high rez digicams sensor). The eye
optics alone, due to spherical aberration and color, reduce this to
about 109 lp/mm. When we add the optics of a 50mm viewer lens we
further reduce resolution at the fovea to ~ 106 lp/mm...this assumes a
very well corrected optic, almost diffraction limited. The
magnification in this case, from film to fovea, is 0.35x, (minify)
assuming an avg fl of the eye at 17mm fl. Using this factor, the 106
lp/mm at the fovea converts to 37 lp/mm on the film. Which is pretty
close to the example above (which we were reality checking here)..... as
if you change the unaided view distance above just a bit, (which were
subjective) the answers will be VERY close.

Interestingly enough, on the USAF glass resolution target, which is used
to check the resolution of an optic...... this value converts to line 2
in the 5 pattern. When I use my 50mm stereo lens over the USAF glass
chrome target on my light box, I can resolve this pattern. (I can see
black lines and white background) So this makes me pretty confident
these numbers are at least in the ballpark, for avg. to good vision,
which I would classify myself as.

So I might have to disagree with your assertion that 56 lp/mm is too
much for the eye to resolve...... but Don, I realize you have had
extensive training and experience in human vision testing through the
years, so if you see any flaws in my interpretation, please note them,
as this is a learning process for all of us.

>
> I am curious about the 60mm fl lens that had a diameter of 4 inches,
> (102mm). Is this a f/0.6 , 'dream', lens ?
>

Yes, as I mentioned in detail in a previous
post..... this lens design would be f.06 if it was used as a camera
lens. But for its intended purpose, as a film loupe, it would become
an f12 lens, assuming a 5mm eye pupil diameter. Re-read my previous
posts for clarification.

> Also, I don't believe that it a fact that most viewers have a, "very low light level".
>

Light levels are subjective Don, 200 years
ago, a good Kerosene lamp was considered very bright. What I referred
to previously was "optimum" lighting conditions for a stereo viewer to
maximize the eyes ability to resolve. This would equate to ~ 60x
brighter than the brightest back light I ever measured in a stereo viewer.

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 00:08:13
From: dlopp2000

Regarding # 2092,
I am curious as to why the 75/30mm achromats on the World 3D viewer
need tight quality controls, as they are relatively simple achromats ?

Also, what does gain by viewing 6 x 7cm chromes with 10X viewer lenses.

Also, contrary to what I read, my corrective eye ware, (2.75 D),
allows me to, easily, view a 19 inch wide print from a distance of 11
inches.

I must turn my eyes, but that is because my eyes can only see (sharp-
ly), about a 2 degree field of view at one time.

I have not bee convinced that digital print 3D offers a higher degree
of resolution than I can see in my MF viewer, when it has 55mm fl,
(4.6X), 0ptics ? My MF viewer cost less than $ 150 to make.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 00:09:44
From: dlopp2000

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 00:32:21
From: dlopp2000

Sorry about the duplication, but the message did not disappear when
I pushed SEND, and it did not show in my send box.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 00:33:31
From: Bill G

Hi Don

> I am curious as to why the 75/30mm achromats on the World 3D viewer
> need tight quality controls, as they are relatively simple achromats ?
>

"tight" ? I was being humorous.... I was
suggesting there is very little, if any, quality control considering
the price they sell the entire viewer at. A doublet has 4 surfaces
which must be ground to a certain scratch / dig tolerance, a given
tolerance on curvature, a tolerance on centration, a tolerance on the
refractive index of each glass and also a tolerance on the lenses
parallelism to the film plane. Even on a simple doublet, many of these
tolerances measure in the .x to .0x mm region, which in the optics world
is not much, but when you when small tolerance errors stack up, you get
all types of unpredictable aberrations. A good optic, such as those
sold by Schneider or Rodenstock or even Edmunds, will always be tested
on an optical test bench using an computerized optical laser system,
which will give readings on the critical factors such as MTF (on and off
axis), fl, BFL, distortion, etc. If the lens does not pass their min.
thresholds, they reject the lenses. These machines cost in the $250k
range. This is also why a an achromat of similar size to a Saturn
doublet will cost about $75 each in volume from a good optics house. I
am guessing the doublet in the 3d World viewer can't be worth me than
$10 each based on the price of the viewer. Not long ago, they were
$29. I was just speculating 3d world is not implementing this level
of QC, but I could be wrong...

> Also, what does gain by viewing 6 x 7cm chromes with 10X viewer lenses.
>

You may want to re-read that post Don,
I mentioned I was inspecting the film with a 10x loupe....I then went on
to say, these are not viewer lens, as they are designed with a very
narrow FOV.

> Also, contrary to what I read, my corrective eye ware, (2.75 D),
> allows me to, easily, view a 19 inch wide print from a distance of 11
> inches.
>

That's excellent Don!!! Have you considered
buying a Mirscope? I still have 20/20 vision, wear no corrective
eyewear, have no astigmatisms, and my closest sharp focus distance is
20" which is about normal for the 45 - 55 year old crowd.

> I must turn my eyes, but that is because my eyes can only see (sharp-
> ly), about a 2 degree field of view at one time.
>

yes, only our Fovea has sharp
vision, however, your corrective eyewear is only optimized for a narrow
FOV, or the glasses would become abnormally heavy and bulky. Opticians
design corrective eyewear for real world use, not wide field stereo
use....i.e. when you view a given subject, you typically turn your
head, so your eyes are relatively straight, not looking 40 degrees
towards the side of your glasses.

> I have not bee convinced that digital print 3D offers a higher degree
> of resolution than I can see in my MF viewer, when it has 55mm fl,
> (4.6X), 0ptics ? My MF viewer cost less than $ 150 to make.
>

It's the difference in print size Don..... if
the original has 50 lp/mm in a 2" square, viewed at a 2" distance (50mm
optic), this is equal to an enlarged print at 20" square, at 5
lp/mm....... 6 of one, half dozen of the other? Make sense? If you
start with the same original, of course you can alter the print size /
view distance to produce equal resolution views.... hope this helps Don...

>
> DON
>
>
>
>
>

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 08:21:34
From: dlopp2000

Regarding # 2101.

I don't consider the assertion that
the 3D World viewer lenses, 75/30mm
are manufactured without a quality
control to be valid.

Also, why should an achromat lens be
tested for MTF, (on and off axis), for
back focal length, distortion, etc ?

These arte not camera taking lenses.

Does anyone believe that the zillions
of stereo viewer achromats, found in
the various stereo viewers were tested
for distortion, etc.

The Saturn, (Edmund),78/46mm, #42792,
2 for $ 295 achromat, with all of its
asserted quality control, produces sig-
nificantly more distortion than does
the 75/30mm lens which has, allegedly,
been produced with little or no quality
control.

Amazing.

As far as me making digital prints, I do
not have any digital equipment, (except
for my computer), or any digital knowledge.

I am completely satisfied with my MF stereo
slides, when I view them in a decent viewer.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 10:09:32
From: Bill G

Hi Don!

>
> I don't consider the assertion that
> the 3D World viewer lenses, 75/30mm
> are manufactured without a quality
> control to be valid.
>

As i suggested Don, I was just speculating,
based on price..... you could be right....it's possible they run these
$8 lenses through a battery of optical tests to assure they meet min.
performance standards.

> Also, why should an achromat lens be tested for MTF, (on and off axis), for back focal length, distortion, etc ?
>

Because, if the lens was built to tolerance
in all areas, then these performance characteristics should be
delivered in the final product. It's a confirmation the lens was
built to spec.

> These arte not camera taking lenses.
>
> An optic is an optic, they all have the same optical principles at play, such as MTF, fl, BFL, distortion, etc. The testing equipment is not aware if its a loupe or a camera lens.
>
> The Saturn, (Edmund),78/46mm, #42792,
> 2 for $ 295 achromat, with all of its
> asserted quality control, produces sig-
> nificantly more distortion than does
> the 75/30mm lens which has, allegedly,
> been produced with little or no quality
> control. Amazing.
>

Distortion is not necessarily a build
defect, rather, it's a necessary evil of optics design...... when you
push a doublet performance in the design process, distortion is a
compromise the lens designer must accept. The purpose of the QC test
is to determine if the final product delivers the proper levels of
distortion the design called for. So because one lens design produces
more distortion than another design, is not proof the higher distorted
lens was not subjected to QC.

> As far as me making digital prints, I do not have any digital equipment, (except for my computer), or any digital knowledge.
>

Most of the photographic community today
does make digital prints Don, hence the beauty of Johns product.

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 11:28:11
From: dlopp2000

Regarding 2101 and 2105.

If Radio Shack reduces the price of a $400 receiver down
to $150, I am to assume that it is cheap because Tandy
cut costs by not having quality controls. In other words,
low cost indicates a lack of quality controls being in
place. Brilliant deduction.

Apparently, I am to assume that the pincushion distortion seen
in the Saturn, (Edmund Optics), 78/46mm achromat was designed
to be a characteristic of the lens. Apparently the lenses did
pass their quality control, (QC), department.

As regards to the print viewer designed by John H, John showed
it to me, and the image was spectacular, but it was not a picture
of a scenic view, so I was not able to compare it with any views
that I am used to seeing in my less than $100 MF viewer.

I have yet to see any prints that offer a viewing experience equal
to what can be seen in a, (back lit), quality MF stereo slide viewer.

I am attempting to deal with the real world.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 11:53:06
From: Bill G

Hi Don!

>
> In other words, low cost indicates a lack of quality controls being in place. Brilliant deduction.
>

Yes, you got it right Don, in optics, often low
cost does equate very minimal if any quality controls, the reason is,
rejection rates drive up prices. This is most pronounced in astronomy
optics....whereas you can find two identical 90mm apt. telescopes, same
f ratio, similar costing glass used in objective lens doublet. Yet,
one of the scopes sells for 4x the price vs. the other? Why? Quality
Control of the optics. The more expensive scopes are subjected to a
series of final testing...and when the glass does not meet all pre set
performance standards, the lenses are rejected, greatly increasing the
cost of the lenses that pass the QC process. So yes, your
understanding was accurate.

You also may find it interesting, that many of these
high-end refractor scope makers, who have rigorous quality controls
produce scopes in the $7k - $10k range, and the wait list to buy one is
in the 5 - 7 year range. So, it does appear, many buyers do have an
appreciation for high quality optics.

As for your analogy regarding Radio Shacks
Tandy line of electronic stereos, it's hard for me to comment. My
comments were directed towards optics, not music systems.

> Apparently, I am to assume that the pincushion distortion seen in the Saturn, (Edmund Optics), 78/46mm achromat was designed to be a characteristic of the lens. Apparently the lenses did pass their quality control, (QC), department.
>

Yes, that is correct. It's not possible
to design a doublet in the 70 - 80mm fl range, to cover MF trannies,
without having distortion. If the lens designer wants to rid, or
significantly lower distortion, than he must start adding more elements
to the design. All optics have have limitations....and the job of the
designer to intelligently trade-off compromises that best fit the
application, based on the number of elements the design has.

>
> I am attempting to deal with the real world.
>

Yes, we all are Don....it's never easy .......

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 20:36:12
From: dlopp2000

Responding to 2108,

I just read that it it is impossible to design a doublet in the 70 to
80mm focal length range to cover MF tranies without distortion. If
this is true, how is it 3D World is able to produce their MF viewer
which does not produce any significant distortion, when compared to
the very significant pincushion distortion which is easily seen in the
Saturn MF viewer ?

Please be so kind as to tell us what kind of significant distortion
you have seen in the 3D World viewer. Is it pin- cushion distortion,
or is it barrel distortion, ?

I don't believe that it is realistic to compare a complex, $7000 to
$10000 high end refractor telescope with a simple, mass produced, $30
MF viewer, when discussing quality control ?

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 21:15:25
From: Bill G

Hi Don!

>
> I just read that it it is impossible to design a doublet in the 70 to
> 80mm focal length range to cover MF tranies without distortion. If
> this is true, how is it 3D World is able to produce their MF viewer
> which does not produce any significant distortion,

Don, you just answered your own
question here.... yes, the 3dWorld doublet has less distortion than the
Saturn doublet, but they both have distortion.... so my assertion
remains. As mentioned, it comes down to trade-offs... the 3dWorld
has many other shortcomings in turn for its "less distortion".

> I don't believe that it is realistic to compare a complex, $7000 to
> $10000 high end refractor telescope with a simple, mass produced, $30
> MF viewer, when discussing quality control ?
>

You are taking what I wrote, completely out of
context. I never made the comparison you suggest above. More
importantly, I can tell you from my experience designing and building
doublets. Lets say the cost of a well designed stereo doublet is in
the $40 each price range made in Asia, volume 500. This price is
through a USA vendor who has off-shore manufacturing, quite common
today.

These USA vendors typically offer a USA QC inspection service, whereas
they test each optic at their facility to meet certain performance
criteria which is agreed upon based on the design. This will add
about $30 to the price of each lens. Part of this $30 is for the cost
to perform the test (maybe 5 minutes per lens with the right
computerized test equipment) and the rest of the $30 goes towards the
rejected lenses, which are not salvageable. However, as a buyer, you
are now assured the lenses you receive will meet a min. performance
specifications. This is what QC is all about Don, and it does not come
for free.

This is why making optics can be a pandoras box.... there is a lot of
links in the chain, any one of the links can reduce yield quantities,
which increases the per unit cost. The more elements in the optic, the
tighter the tolerances the greater the rejection rates, the higher the
costs. In low end optics, nothing is wasted, and sometimes there is
no real testing of the optics, other than maybe a quick visual before
the product is boxed.

So Don, based on the pricing above from my previous experience
designing and building doublets...... I assumed the 3dWorld lenses at
$10 each would not have enough dollars in their budget to justify much
QC. Is this assumption wildly off-base? Possibly I am drawing a
foolish conclusion from my experience? I remain open Don.

Bill

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 22:40:59
From: dlopp2000

Regarding No. 2110,

I was surprised to read that the 3D World viewer, 75/30mm lenses
do have distortion, but I referred to, "significant distortion", and
asked whether, the alleged distortion", was of the pincushion, or
barrel type.

NO ANSWER.

Edmund Optics sells a 75/30mm achromat, # M32-498 for $65.10, and it
is worse than the Saturn 78/46mm as regards to pincushion distortion.
So much for the, alleged, advantages of quality control.

DON

Subject: Re: A properly designed MF viewer.
Date: 2008-07-28 23:55:29
From: Bill G

Hi Don!

>
> I was surprised to read that the 3D World viewer, 75/30mm lenses
> do have distortion, but I referred to, "significant distortion", and
> asked whether, the alleged distortion", was of the pincushion, or
> barrel type.
>
> NO ANSWER.
>

Don, I am very sorry I missed answering
one of your questions. To date, i have answered every question you
ask, in detail....some of them, I have answered at least 3x. It's
exhausting, please have some compassion for me, age is catching up to
me, occasionally I slip up.

ANSWER = Pincushion

> Edmund Optics sells a 75/30mm achromat, # M32-498 for $65.10, and it
> is worse than the Saturn 78/46mm as regards to pincushion distortion.
> So much for the, alleged, advantages of quality control.
>

I explained this 3x times previously
Don.... in short, distortion has NOTHING to do with QC...... the purpose
of QC is to check that all the performance specifications of the
finished lens are within the design tolerances. (which confirms the
lens was built to spec.) Distortion is one of those performance
specifications. Distortion is almost always a part of a design, its
nearly impossible to HAVE 0.00 distortion, specially with a doublet for
MF viewer.

I have some $600+ telescope Eye
Pieces. They go through rigorous QC testing, hence their price. The
distortion in these EP's are EXTREME, barrel, rectilinear kidney bean
distortion, etc. A brick wall looks like it has swirls in it :-).
These are not defects which QC should have caught....instead, they are
compromises the lens designer had to make to assure he hit the more
important benchmarks for astronomy viewing, such as AFOV, resolution,
contrast, etc.

As I described in my earlier post, we
know the exact distortion a lens should have before it's built. I
included this pix previously, so you could see a graphical
representation of the distortion in the design stage. This distortion
is part of the design, not a defect, therefore QC will not catch-it
(assuming its within +/- % tolerance) Matter of fact, if there was no
distortion in the final lens, the QC would kick the lens out, as it
means the lens was not built to spec., and other performance variables
will suffer accordingly..... have a look again.

*http://tinyurl.com/59o5fw

I hope this clears up any confusion over
distortion being a design constraint. Any further questions Don, I
suggest you write me off list, as we must be careful abusing this
subject on the list, as the moderator may remove us from the list.....
OK?

Bill

*