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Subject: More on wide angle viewing
Date: 2012-01-16 20:06:56
From: John Thurston
Back in September of 2011, Don Lopp mentioned his wide angle viewer with
an effective 45mm focal length.

http://tech.groups.yahoo.com/group/MF3D-group/message/3592
- or -
http://tinyurl.com/72hshef

I had a phone conversation with Don in November on this subject and
decided to re-create his concept. I talked a little about this in my
posting earlier in January.
http://tech.groups.yahoo.com/group/MF3D-group/message/3877

My prototype is really the front half of a sliding-box viewer (think
Saturn Viewer). I didn't want to invest in the back-half until I
determined if the optics were correct. I've had some independent
feed-back which makes me think I should proceed. Before I do, I wanted
to bounce some ideas off the group.

If I'm building a one-off viewer for myself, I'll probably proceed with
the sliding-box design. I may incorporate illumination, or may leave
that for a later date and first build it as a steal-the-light unit.

Is anyone else interested in a heavy, _wide_ angle viewer? If so, I'd
like to hear your desires and limitations. Is a sliding-box design
sufficient for your needs? Does it need to be illuminated, or is STL
sufficient? Do you want a finished work of art, or kit from which you
can build your own?

I usually throw my projects out to the group on a cost-recovery basis.
How much are you willing to spend? When I'm all done with mine, I think
I will have spent $350 and invested a couple of months of design work.
--
John Thurston
Juneau, Alaska
Subject: Re: More on wide angle viewing
Date: 2012-01-17 05:44:00
From: narjan@pipeline.com
>From: John Thurston <juneau3d@thurstons.us>

>My prototype is really the front half of a sliding-box viewer (think
>Saturn Viewer). I didn't want to invest in the back-half until I
>determined if the optics were correct. I've had some independent
>feed-back which makes me think I should proceed. Before I do, I wanted
>to bounce some ideas off the group.

"I'm rubber, you're glue, bounces off me...."

BTW, what lenses/combination of lenses have you settled on ?
in case other members of this group wish to "peer review"
your work by giving them a quick try.

Best Wishes,
John Billingham
Subject: Re: More on wide angle viewing
Date: 2012-01-17 05:52:51
From: narjan@pipeline.com
>>From: John Thurston <juneau3d@thurstons.us>
>
>>My prototype is really the front half of a sliding-box viewer (think
>>Saturn Viewer). I didn't want to invest in the back-half until I
>>determined if the optics were correct. I've had some independent
>>feed-back which makes me think I should proceed. Before I do, I wanted
>>to bounce some ideas off the group.
>
>"I'm rubber, you're glue, bounces off me...."
>
>BTW, what lenses/combination of lenses have you settled on ?
>in case other members of this group wish to "peer review"
>your work by giving them a quick try.
>
>Best Wishes,
>John Billingham
Subject: Re: More on wide angle viewing
Date: 2012-01-17 06:02:39
From: narjan@pipeline.com
>From: John Thurston <juneau3d@thurstons.us>

>My prototype is really the front half of a sliding-box viewer (think
>Saturn Viewer). I didn't want to invest in the back-half until I
>determined if the optics were correct. I've had some independent
>feed-back which makes me think I should proceed. Before I do, I wanted
>to bounce some ideas off the group.

"I'm rubber, you're glue, bounces off me...."

BTW, what lenses/combination of lenses have you settled on ?
in case other members of this group wish to "peer review"
your work by giving them a quick try.

Best Wishes,
John Billingham
Subject: Re: More on wide angle viewing
Date: 2012-01-17 12:09:09
From: John Thurston
narjan@pipeline.com wrote:
>
>> From: John Thurston <juneau3d@thurstons.us>
>
>> My prototype is really the front half of a sliding-box viewer (think
>> Saturn Viewer). I didn't want to invest in the back-half until I
>> determined if the optics were correct. I've had some independent
>> feed-back which makes me think I should proceed. Before I do, I wanted
>> to bounce some ideas off the group.
>
> "I'm rubber, you're glue, bounces off me...."
>
> BTW, what lenses/combination of lenses have you settled on ?
> in case other members of this group wish to "peer review"
> your work by giving them a quick try.

I have used (per Don's suggestion) objectives from surplus
7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
length, coated achromats.
The eyepieces are coated, achromats which are 39mm diameter,
60(ish)mm focal length.

FWIW, this combination was "settled" on by being an
affordable and available combination which seems to work. It
wasn't arrived at through ray-tracing and numerical
analysis. I'm sure there is someone who can do the numbers
and demonstrate that the combination is sub-optimal and
could be improved. I'm pursuing something which can actually
be built rather than achieving design perfection.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us
Subject: Re: More on wide angle viewing
Date: 2012-01-17 13:52:15
From: narjan@pipeline.com
From John Thurston:

>Back in September of 2011, Don Lopp mentioned his wide angle viewer with
an effective 45mm focal length.

and...

>I have used (per Don's suggestion) objectives from surplus
>7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
>length, coated achromats.
>The eyepieces are coated, achromats which are 39mm diameter,
>60(ish)mm focal length.
>

Oh ! 60mm is a bit longer than 45mm, I'd hoped you'd bumped into
"just" the right combo of "Surplus Shed" lenses.

I've had the honor (courtesy of Jim Harp) of viewing through a
Don Lopp "Loppomatic" viewer and it was a wonderous treat.

When asked about lenses, Don apparently said, "Oh, just something from
the surplus store" (I'd KILL for THAT surplus store !)

Has anyone here asked the folks at "Surplus Shed" to have a shot at making
a 45mm wide field viewer lens ? I know they make up nice microscope
lenses with combos of surplus items which you can buy a a "kit"
or assembled.

Yours in cheap optics,
John Billingham
Subject: Re: More on wide angle viewing
Date: 2012-01-17 14:33:32
From: John Thurston
narjan@pipeline.com wrote:
> From John Thurston:
>
>> Back in September of 2011, Don Lopp mentioned his wide angle viewer with
> an effective 45mm focal length.
>
> and...
>
>> I have used (per Don's suggestion) objectives from surplus
>> 7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
>> length, coated achromats.
>> The eyepieces are coated, achromats which are 39mm diameter,
>> 60(ish)mm focal length.
>>
>
> Oh ! 60mm is a bit longer than 45mm, I'd hoped you'd bumped into
> "just" the right combo of "Surplus Shed" lenses.

Errm. I'm not sure you're following. One of the elements has
a focal length of 60mm, but the effective focal length of
the viewer is much shorter than that.

This is a compound element design. For each eye, there are
two achromatic elements. In each eye's light path is a 190mm
objective and a 60mm eyepiece. When spaced 25(ish)mm apart,
this gives an effective focal length of about 45mm.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us
Subject: Re: More on wide angle viewing
Date: 2012-01-17 15:21:32
From: Bob Venezia
...and just to chime in, i have seen several Don Lopp viewers, including his latest, and i've seen john thurston's prototype, which was an attempt to match Don's latest.

Don's latest, as he would tell you, beats the pants off any of his previous viewers. John Thurston's viewer is in the same league, optically. John Thurston's glass seems to be much heavier than Don's though.

If previous viewers could be compared to flake cocaine, these would be crack.

Don Munsil has also gotten to see these viewers. Perhaps he can weigh in.

Bob Venezia
Seattle, Washington
Sent from my iPhone

On Jan 17, 2012, at 12:33 PM, John Thurston <juneau3d@thurstons.us> wrote:

 

narjan@pipeline.com wrote:
> From John Thurston:
>
>> Back in September of 2011, Don Lopp mentioned his wide angle viewer with
> an effective 45mm focal length.
>
> and...
>
>> I have used (per Don's suggestion) objectives from surplus
>> 7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
>> length, coated achromats.
>> The eyepieces are coated, achromats which are 39mm diameter,
>> 60(ish)mm focal length.
>>
>
> Oh ! 60mm is a bit longer than 45mm, I'd hoped you'd bumped into
> "just" the right combo of "Surplus Shed" lenses.

Errm. I'm not sure you're following. One of the elements has
a focal length of 60mm, but the effective focal length of
the viewer is much shorter than that.

This is a compound element design. For each eye, there are
two achromatic elements. In each eye's light path is a 190mm
objective and a 60mm eyepiece. When spaced 25(ish)mm apart,
this gives an effective focal length of about 45mm.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Subject: Re: More on wide angle viewing
Date: 2012-01-17 15:26:47
From: narjan@pipeline.com
>Errm. I'm not sure you're following. One of the elements has
>a focal length of 60mm, but the effective focal length of
>the viewer is much shorter than that.
>
>This is a compound element design. For each eye, there are
>two achromatic elements. In each eye's light path is a 190mm
>objective and a 60mm eyepiece. When spaced 25(ish)mm apart,
>this gives an effective focal length of about 45mm.


Well, then, Errm, EXCELLENT !
you have now answered my original question.

Thanks Very Much,
John Billingham
Subject: compound optics vs. magnifier
Date: 2012-01-17 19:32:48
From: Bill G
I realize technical input was not welcome.... but for those who might be interested......

There is confusion here between fl and AHFOV (Apparent Horizontal Field of View, expressed
in degrees). AHFOV is what the degrees of projection onto the retina, which is the
Immersive effect, or Imax effect, the Holy Grail everyone chases in film viewers. With
a magnifier type of optic, (often called a loupe in photo field), the optical fl and and
the AHFOV are inversely proportional (not perfect, but relatively close).

In a compound optical system, (also called a relay system) in this case binoculars, which
consist of an objective lens which projects its focal plane into the field stop of an
eyepiece, the viewing AHFOV has NO relationship to the effective fl of the two combined
optics. The AHFOV is determined by the eyepiece design, and remains fixed, regardless of
the the fl or the size of the subject its viewing. The subject size (film area) is
limited by the field stop diameter (imaging circle diameter), but the AHFOV is limited by
the design of the Eye Piece. As an example, if you take a given design group of
eyepieces which range in fl's from say 5mm, to 50mm, they will all produce the identical
AHFOV as they have the same optical design. So there is NO difference in immersion
effect (AHFOV) between a 5mm fl eyepiece, and a 50mm fl eye piece of the same design.
The only difference is, the 5mm eye piece will view a much smaller area of the film, (in
astronomy this is the field stop diameter, in photography, the imaging circle) and spread
it out over the same AHFOV. Therefore, a lower fl eyepiece, will produce greater image
magnification on the retina, but the retinal image area remains the same. The Imax
effect (AHFOV) occurs when you "light-up" a larger area of the retina.

In the case of low cost binoculars, their HFOV is often limited, as the cost of any
optical system increases dramatically as the as the HFOV increases, as it becomes more
difficult to control aberrations with wider fields. Most low cost Chinese binoculars I
have seen, typically have 40 deg HFOV, maybe a few might approach 45 deg HFOV. A 3dWorld
viewer produces about a 36 deg AHFOV. Better German binoculars in the $600+ region
produce ultra sharp 50 deg HFOV. While a few of the NEW Canon L binocs $1k - $2k
produce a whopping 65 deg AHFOV.

Unfortunately, these AHFOV values are circles, not squares (like 3dWorld apt. openings
are). Simple math, if you put a square inside a circle, all legs of the square are .70
of the circle diameter (or film diagonal). In which case, you must reduce the AHFOV
degrees listed above by 30%. This is what you would experience on the retina as the
square film reduced the amount of horiz. retina area.

In addition, AHOV is effective by the amount of Eye Relief (ER) designed into the optical
system). Low cost binoc. and telescope eye pieces have very small ER, typically 12mm.
If you wear corrective eye-wear, you must view much further way from the optic, which can
further reduce the AHFOV due to vignetting. But even worse, telescope / binocular
eyepieces are designed to view through the center of the lens, which is the ONLY area
they optimize the design. The reason is, if you want to view subject near the edge, you
simply point the binoculars / telescope till the subject is in the center of the viewing
circle. This is where 3d optics vary so differently from standard viewing optics...with
a stereo viewer, you must swivel your eyes, to see the edges, which forces your eyes to
view through the entire radius of the eyepiece. This is what makes stereo viewing
optics so unique and complex, unfortunately.

I have NO IDEA the details of the optics the OP is using with his project.... he might
have a the worlds best MF 3d optics.... I have NO reason to doubt his assessment. What
I wrote above is just a clarification of the of the terms that are often improperly
expressed, such as fl, AHFOV, immersiveness, effective fl, etc.

Regards
Bill G


On 1/17/2012 12:33 PM, John Thurston wrote:
>
> narjan@pipeline.com wrote:
> > From John Thurston:
> >
> >> Back in September of 2011, Don Lopp mentioned his wide angle viewer with
> > an effective 45mm focal length.
> >
> > and...
> >
> >> I have used (per Don's suggestion) objectives from surplus
> >> 7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
> >> length, coated achromats.
> >> The eyepieces are coated, achromats which are 39mm diameter,
> >> 60(ish)mm focal length.
> >>
> >
> > Oh ! 60mm is a bit longer than 45mm, I'd hoped you'd bumped into
> > "just" the right combo of "Surplus Shed" lenses.
>
> Errm. I'm not sure you're following. One of the elements has
> a focal length of 60mm, but the effective focal length of
> the viewer is much shorter than that.
>
> This is a compound element design. For each eye, there are
> two achromatic elements. In each eye's light path is a 190mm
> objective and a 60mm eyepiece. When spaced 25(ish)mm apart,
> this gives an effective focal length of about 45mm.
> --
> John Thurston
> Juneau Alaska
> http://stereo.thurstons.us
>
>
Subject: Re: More on wide angle viewing
Date: 2012-01-17 19:55:16
From: bill_in_3d
--- In MF3D-group@yahoogroups.com, John Thurston wrote:

> > From John Thurston:

> >
> >> I have used (per Don's suggestion) objectives from surplus
> >> 7x50 binoculars. These are 52mm diameter, 190(ish)mm focal
> >> length, coated achromats.
> >> The eyepieces are coated, achromats which are 39mm diameter,
> >> 60(ish)mm focal length.
> >>

< < SNIP > >

John,

Given the high level of interest already expressed, could we impose on you for the details of what binoculars you sacrificed to the cause ?

I for one would like to have a design that better approaches the LEEP promise, and wish a place in line if you're thinking of selling the plans for anything good enough to deserve your endorsement.

Also, can you comment if you are looking from a very small distance to the eyepiece, what Bill Glick called "Eye Relief" ?

Thanks in advance.

Bill W
Subject: Re: compound optics vs. magnifier
Date: 2012-01-17 20:07:46
From: John Thurston
On 1/17/2012 4:32 PM, Bill G wrote:
> I realize technical input was not welcome.... but for those who might be interested......

I never meant to imply that technical input was not welcome.
I only hoped that people would realize that what I hacked
together was done without any pretense of being technically
correct. It's a hack of available optics which is not the
same as a carefully designed system.

Now, I'm gonna read the rest of your message and see if I can
relate it to my hack.
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us
Subject: Re: compound optics vs. magnifier
Date: 2012-01-17 21:22:07
From: timo_puhakka
--- In MF3D-group@yahoogroups.com, John Thurston wrote:
>
> I never meant to imply that technical input was not welcome.
> I only hoped that people would realize that what I hacked
> together was done without any pretense of being technically
> correct. It's a hack of available optics which is not the
> same as a carefully designed system.

I am sure that I am not the only one who would like to make my own wide angle MF slide viewer. With that in mind, I would like to know what sort of eyepieces you are using. Telescope? Microscope? or the Binocular eyepieces? Binocular objectives would seem to be a no brainer.

Timo
Subject: Re: compound optics vs. magnifier
Date: 2012-01-17 21:27:28
From: John Thurston
On 1/17/2012 4:32 PM, Bill G wrote:
> I realize technical input was not welcome.... but for those who
> might be interested......
>
> There is confusion here between fl and AHFOV (Apparent Horizontal
> Field of View, expressed in degrees). AHFOV is what the degrees of
> projection onto the retina, which is the Immersive effect, or Imax
> effect, the Holy Grail everyone chases in film viewers. With a
> magnifier type of optic, (often called a loupe in photo field), the
> optical fl and and the AHFOV are inversely proportional (not perfect,
> but relatively close).

If apparent horizontal field of view is the value of interest, how
should I measure it?
--
John Thurston
Juneau, Alaska
Subject: Re: More on wide angle viewing
Date: 2012-01-17 21:45:23
From: John Thurston
On 1/17/2012 4:55 PM, bill_in_3d wrote:
> Given the high level of interest already expressed, could we impose on you for the details of what binoculars you sacrificed to the cause ?

I started by hitting my local hock-shop and buying a pair of 7x50 B&L
WWII, binoculars. When I got them home, they were so clean, so well
adjusted and so nice that I couldn't bring myself to strip them of their
objectives :(

In their place, I ordered some used/take-out objectives from Surplus
Shed (Item No: L1380). I ordered four in the hopes of getting two which
would serve.

I tried placing several different lenses in front of them for use as an
eyepiece. I have several pieces of glass around here and just tried what
I had. This was _not_ a scientific process. The one I ended up liking
best was a 39mm diameter achromat. I suspect it is similar (or
identical) to L11519, I can't remember where I got these lenses.

The two lenses are spaced almost as close as possible to each other. In
fact, while I was playing with them, I just stacked the eyepieces right
on top of the objectives. I followed this up by "mounting" the lens
elements in pieces of wood so I could play with their relative distances
(I don't own an optics table).

- snip -
> Also, can you comment if you are looking from a very small distance to the eyepiece, what Bill Glick called "Eye Relief" ?

I don't have the viewer in my possession at the moment so can't say
exactly what eye-distance I was using. My eyes are well enough matched
that I don't wear glasses when viewing. This means I can suck right up
to the eyepieces and eye-relief isn't a big concern to me. I realize
that is is for others.


--
John Thurston
Juneau, Alaska
Subject: Re: compound optics vs. magnifier
Date: 2012-01-17 23:02:03
From: Brian Reynolds
John Thurston wrote:
>
> If apparent horizontal field of view is the value of interest, how
> should I measure it?

Sky & Telescope has an eyepiece primer:

<http://www.skyandtelescope.com/equipment/basics/3311076.html>

Televue has an on-line eyepiece calculator:

<http://televue.com/engine/TV3_page.asp?id=89&plain=TRUE>

and an article on choosing eyepieces:

<http://televue.com/engine/TV3_Page.asp?id=79&plain=TRUE>

Both sites have a lot of other information on eyepieces and optics.

--
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: compound optics vs. magnifier
Date: 2012-01-17 23:02:18
From: Bill G
>
> If apparent horizontal field of view is the value of interest, how
> should I measure it?
>

I read your other post, ... problem is, I am not sure the system you rigged up is
performing as compound optic..... what usually dictates this, is the distance between the
objective and the eyepiece (EP). The objective lens will deliver a focused image at its
fl distance. This is where the eyepiece would would accept this image, and magnify
it. Also, on the subject side of the objective lens, binoc objective lenses are
designed for infinity subjects, not subjects an inch away. If you just randomly used an
objective lens, well, even worse, you have NO idea the design criteria of the lens. You
might be calling it an objective lens, but it can could have been designed to perform a
completely different function. It could have been used for a specific purpose, such as
in a copy machine, which is one of the places many spare optics get dumped from. They
are often rejects, as its cheaper to build large quantities of low tolerance optics and
simply test them, and toss the bad ones vs. high tolerance manufacturing.

If you are simply stacking the EP atop the objective lens, it will surely be a witches
brew to deal with. If you have a true compound optic, it will produce a clearly defined
projected circle (exit pupil) through the EP, you can see this in a dark room with a light
at the film end, and a Ground Glass on the other end. If you converted it into a
magnifier, you will not have a clearly defined exit pupil. If you have a magnifier,
its impossible to measure unless you have an excellent collimated light source, in which
case, you can follow the instructions below. Assuming you have a compound optic, I can
explain how to measure if they exist in a binoc, you can figure out how to transpose this
technique to whatever set up you have, assuming its performing as a compound optic.

First, the HFOV is often taken from the design spec, when not
available, to be accurate, HFOV is measured by an optical laser tester....the entire MTF
curve of a built lens, including all its performance specs can be accomplished in less
than a minute....this assumes the lens is in "working condition"...

as for a home-brew method, assuming its a compound optic, it can be attempted, but not
easy, but with some luck, you can get close if you are diligent enough with measurements,
....

1) shine a diffused light source into the objective, work in a relatively dark area.
Use a Ground Glass that is as fine as you can get.... use glass with very fine diamond
sharpening particles (1/4 micron or smaller) to make one. The glass needs to be thin as
possible, 1/16" or thinner.

2) Place GG over eyepiece... the exit pupil (light path) in a compound optic is clearly
defined, unlike a magnifier. Stand binocs upright, objectives facing down. Use the GG
position as a reference measurement position.


3) Raise the GG up until the circle of projected light on the GG becomes its absolute
smallest circle. Measure GG distance from the reference position, add back the thickness
of the GG. This is the ER measurement.

4) From the ER position, continue moving the ground glass upwards, till about an inch
atop the ER position. Measure the diameter of the image circle projected onto the GG,
from there, its simple right angle trig to determine the HFOV angle. You have a one
known angle, 90 deg., two known leg distance (ER to top of GG raised past the ER
position) and halve the diameter of the circle. Enter into any right triangle
calculator, or do the trig to find the angle at the center axis of the eye piece to the
edge of the projected circle.... multiply by 2 to cover the other side, and you will be in
the ball park.

I have tried this with an optical bench, with very fine measuring instruments, and
typically the best I could accomplish was +/- 20%. vs. laser testing. Trying to
accomplish this with just your hands, well, you need many hands, and they have to be ultra
steady...as every mm of measurement is critical and the slightest movement of the GG
changes measurements, so it helps to have the binocs fixed, and the GG on a moving fixture
which remains co planar with the surface of the eyepiece. And when I test things like
this, all my elements are in a high tolerance concentric barrel, as the spacing between
the elements and their axis being concentric would be mandatory, otherwise the
measurements are useless.... as you can not build the next one wtihin the same
tolerances, then the performance variables change.

Or, just tell me how much the binocs cost, I can get you within +/- 20%. Typically low
cost binocs are designed with the prisms limiting the HFOV that can be passed through to
the eyepiece, usually 40 deg max. Some as low as 25 deg.

If you want to test just the EP, pass collimatted light through the EP and do the same as
above....

The likelihood of hacking something like this together and getting less than 15%
distortion, would prob. be... in 1 in 100k, or prob. worse. This assumes you are
getting the VERY wide Image you stated initially.....

Hope this helps...


Bill







>
Subject: Re: More on wide angle viewing
Date: 2012-01-17 23:33:46
From: Bill G
> I don't have the viewer in my possession at the moment so can't say
> exactly what eye-distance I was using. My eyes are well enough matched
> that I don't wear glasses when viewing. This means I can suck right up
> to the eyepieces and eye-relief isn't a big concern to me. I realize
> that is is for others.
>
>
Its not just about ER.... is your unaided vision corrected at
infinity? Then if the set-up you used, assuming film was in focus, was delivering a ray
pattern inverse to your refractive error, and others who might not share your same
refractive error would never get the film in focus. As the system you have working for
your eyes, is set at ONE focus position. Since the system was not designed as a single
optical unit, you would have no way to know how to move the elements to and fro each other
to achieve focus. This is the beauty of a simple optic, like a doublet, just move the
lens to and from the film...and even then, often there can not be more than a diopter of
correction before the IQ falls apart.


Next, try viewing the optic with your eye pupil non-concentric with the lens center.
What happens to the image? This must be accounted for, unless you have an IPD adjust on
the viewer to assure concentricity.... this is by far one of the most complicated issues
for a stereo viewer optic, any optic with decent I. Q. DEMANDS your eye be concentric,
hence why even cheap binocs have IPD adjust.

Have you viewed graph paper on a light box yet? That should give you a feel for the
amount of distortion and the distortion locations / types. Does some of the distortion
appear as ocean waves moving to and from the graph paper on the Z-Axis? Now move your
eye a mm or two in each direction, see what happens to that distortion, does it shift?
This will often create distortion rivalries, headache city....

Try putting some small text under your set-up.... find someone with no accommodation
remaining in their vision, typically 60 - 65 + years of age.... get the center sharp,
rotate eye out on the radius in all directions, does it remain sharp? If not, this means
your optic does not have a flat field, and the eye most accommodate (re-focus) while
scanning around the lens radius....if you have some accommodation remaining, say a few
diopters, it might work for you, but not someone who has little or no accommodation
remaining.

Try moving your eye back from the glass, as if you were wearing corrective eye wear...
does the image go soft? Do the distortions change? (keep graph paper on the light box)
Does the image vignette and you can not see the edges of the apt. openings?

Anyway, those are just a few home-brew tests you can try to see if you hit the lottery
with your design.....

A much simpler approach to a wider FOV is to view larger images with simpler optics, but I
know how inconvenient it is to transfer the film into a different format size.

Back in my early days of having optics designed for film viewers, about 10 yrs ago, I
built a a 75mm fl Achro doublet that would view wider film, about 50x60mm.... I had to let
distortion go a bit to reduce aberrations.... about 5% in the very corners mostly.....
which I could have masked. But at 43 deg HFOV, it was lot of bang for such a low
tolerance, relatively low cost optic. Prob. $100 each with enough volume. Of
course the Image Quality is NO match for my 5 - 6 element designs I later built, but the
cost is about 10x as you need sophisticated barrels in addition to the elements...

I later had designed (but never built) a 56x100 triplet, which would have been the
ultimate film format, as it matches well with HD tv aspect ratio. But I got burnt out
with film, as 3dtv was surfacing, seeing digital is the future.... that design was the
culmination of nearly a 10 yr journey.... one I wish I never started.

Bill G





>
>
Subject: Re: compound optics vs. magnifier
Date: 2012-01-17 23:43:50
From: Bill G
> Televue has an on-line eyepiece calculator:
>
> <http://televue.com/engine/TV3_page.asp?id=89&plain=TRUE
> <http://televue.com/engine/TV3_page.asp?id=89&plain=TRUE>>
>

Just so ya don't confuse John any further, these calculators do NOT calculate what John
was seeking....the ER and HFOV is fixed in the design, there is nothing to calculate, you
either know it from the design spec, or you measure it. Just glance at any class of Eye
Piece on their web site, you will see each class has a fixed AFOV (in astronomy, its AFOV
as they don't view a square)..... the ER does change a bit between fl's. But you can not
calculate it, its part of the optical design.

Astronomy EP's are very poor choices for film viewing, as most have have let distortion
go, as when viewing the night sky, you have no reference of the star locations, so if they
are off 10%, it won't effect the WOW factor, try that in a stereo viewer....

>
> and an article on choosing eyepieces:
>
> <http://televue.com/engine/TV3_Page.asp?id=79&plain=TRUE
> <http://televue.com/engine/TV3_Page.asp?id=79&plain=TRUE>>
>
> Both sites have a lot of other information on eyepieces and optics.
>

Eyepieces designed to be used in a telescope which delivers an image circle to match an
industry standard size, which is pre determined based on 2" or 1.25" standard size EP's.
..... hence why this data is not relevant.... not too mention, most all TeleVues eyepieces
have internal field stops, which means to view film, you would have remove some of the
bottom elements and place the film inside the barrel. This is just one of many reasons why
the widest and latest designed astrononmy eyepieces ($700) are not suited at all for
viewing film...


Bill G





>
> --
> Brian Reynolds | "It's just like flying a spaceship.
> reynolds@panix.com | You push some buttons and see
> http://www.panix.com/~reynolds/ <http://www.panix.com/%7Ereynolds/> | what happens." --
> Zapp Brannigan
> NAR# 54438 |
>
>