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Subject: Ortho
Date: 2011-10-14 00:06:15
From: Don Lopp
What does the width of the stereo image have to do with being an 'ortho'
image ? Just curious !
Subject: Re: Ortho
Date: 2011-10-14 09:03:01
From: Bill G
On 10/13/2011 11:31 PM, Don Lopp wrote:
>
> What does the width of the stereo image have to do with being an 'ortho'
> image ? Just curious !
>

Nothing! Heck, this is stereo 101.... maybe this explains some of the massive confusion on
the more complex topics?

bill


>
Subject: Re: Ortho
Date: 2011-10-14 12:08:31
From: JR
I am glad that the subject heading has been simplified to the word "ortho".   It appears to be the focal point of this discussion.   (is that a pun?)

Anyway, yes Don, it was me, not Bill who erroneously suggested the use of camera lenses for a viewer.   In an offline letter, Don very correctly pointed out that the problem with that is viewing angle; that it would not be possible to see the entire slide (69mm was being quoted at that point) with that focal length (47mm or 50mm depending on whether it came from Don or Bill).   (Thank you, Don),

I did a test with a 50mm camera lens, and verified that what Don said was true.   Then, I got to thinking about why (aperture limitation in relation to back focal distance), and why this "perfect" situation - same lens for viewing as acquiring the original image - would not work. 

It all got back to the concept of "ortho", that is, the same focal length for viewing as for shooting.   And, the question that occurred to me is whether that is actually the case.  

Here is why it may not be:  When you are shooting you are focusing the image on a photosensitive surface (this is the same whether you are using a digital sensor or film).   That image is at a backfocal distance from the nodal point that is equal to (at infinity) or greater than the focal length (for anything closer to the camera than infinity).    So much for optics 101.

Now, if we just replace the photosensitive surface with the slide imaged by that surface, and look back though the same lens, we have the same focal length, and an "ortho" situation, right?   Wrong.   The "gotcha" here is that it is no longer the same focal length.   Here is the reason:  As soon as we look through the camera lens we are effectively changing its focal length, or to be more exact, the focal length of the entire "optical system".

There is another lens in addition to the camera lens, in between that lens and our own photosensitive surface, the retina of our eye.   That is our eye lens.   It would seem to me, that for a viewing system to be considered "ortho", you would have to include all optical elements, including our eye lens.  This changes the effective focal length of the "system".   It becomes a combination of the viewer lens plus the eye lens (and anything else in the light path, like the cornea, the eye fluid or vitrous humour, even the film of  tear liquid or scleral fluid in front of the eye lens).  Lets not even raise the point that the person doing the viewing may, or may not, also be wearing corrective eyeglasses.  All of this, in addition to the viewer lens, combines for the actual focal length of what we "see" when we look into a viewer.

In a previous comment, I raised the question as to whether the so-called "ortho" condition was really all that important (no one has answered this yet).   In any case, I do think that we have to come to agreement as to what we are calling "ortho", and then move on as to a discussion of whether it really is necessary, followed by a very practical discussion of the optimal viewer design (actually, optimal compromise, which is what all optical designs are intended to be).  In this discussion, we should consider all factors, physical as well as optical.  

What, for example, should be the maximum image size (6x4.5, 6x6, 6x7, 6x9, even 6x12?), something else?   Focal length (and perhaps more important, back focal distance), Immersion, accommodation for people who wear eye glasses, ambient light considerations (especially for eyeglass wearers, where light leaks in behind as well as in front of the glasses), and the myriad of other considerations.   

Oh, and how about a new subject heading, like "The ideal medium format stereo viewer".

Bill, Don, and all of you brilliant "lurkers" out there who could contribute ideas, what are your thoughts on this?

JR 

On Fri, Oct 14, 2011 at 8:03 AM, Bill G <bglick@rconnects.com> wrote:


On 10/13/2011 11:31 PM, Don Lopp wrote:
>
> What does the width of the stereo image have to do with being an 'ortho'
> image ? Just curious !
>

Nothing! Heck, this is stereo 101.... maybe this explains some of the massive confusion on
the more complex topics?

bill


>


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Subject: Re: Ortho
Date: 2011-10-14 15:42:20
From: Don Lopp
On 10/14/11 11:08 AM, JR wrote:
> I am glad that the subject heading has been simplified to the word
> "ortho". It appears to be the focal point of this discussion. (is
> that a pun?)

> Anyway, yes Don, it was me, not Bill who erroneously suggested the use
> of camera lenses for a viewer. I disagree as Bill did, IMO, take possession of your remark,
regarding the use of camera taking lenses as being suitable for use as
viewer lenses on Oct 12, 2011 at 1 PM PDT.

> It all got back to the concept of "ortho", that is, the same focal
> length for viewing as for shooting. And, the question that occurred to
> me is whether that is actually the case.
>
> Here is why it may not be: When you are shooting you are focusing the
> image on a photosensitive surface (this is the same whether you are
> using a digital sensor or film). That image is at a backfocal distance
> from the nodal point that is equal to (at infinity) or greater than the
> focal length (for anything closer to the camera than infinity). So
> much for optics 101. Which nodal point are you talking about ? Must we now measure focal
lengths to an accuracy of hundredths of a milimeter?

Apparently we are, now, parsing the word "ortho", into requiring
the measurement of the focal length of the viewer lenses. I can remember
being advised to always remember the word KISS, Keep It Simple, Stupid.
>
> Now, if we just replace the photosensitive surface with the slide imaged
> by that surface, and look back though the same lens, we have the same
> focal length, and an "ortho" situation, right? Wrong. The "gotcha"
> here is that it is no longer the same focal length. Here is the
> reason: As soon as we look through the camera lens we are effectively
> changing its focal length, or to be more exact, the focal length of the
> entire "optical system". Why and how are we able to look through the camera lens, especially if
it has a focal length of 47mm ?

It would seem to me, that for a viewing system to be considered "ortho",
you would have to include all optical elements, including our eye lens.

This changes the effective focal length of the "system". The system
does have a focal length ? How is it measured ?
It becomes a combination of the viewer lens plus the eye
> lens (and anything else in the light path, like the cornea, the eye
> fluid or vitrous humour, even the film of tear liquid or scleral fluid
> in front of the eye lens).News to me.

Lets not even raise the point that the
> person doing the viewing may, or may not, also be wearing corrective
> eyeglasses. All of this, in addition to the viewer lens, combines for
> the actual focal length of what we "see" when we look into a viewer.
In other words there are zillions of variables that must be taken in
to account before a determination as to what is an "ortho" condition.
(Don't forget the air temprerature). If this is the case, would "we" not
be better off if "we" we discontinued the use of the allegedly
un-defineable word "ortho".

THE question at hand was, "How is it possible to view a 3d image in
ortho, taken with a 47mm lens when the image is 69mm wide."

Will a Saturn MF viewer or a 3D World MF viewer provide an ortho view- I
don't think they will, as they both contain 75mm to 84mm focal length
viewing lenses, more than 50 percent longer than are the previously
described 47mm fl camera taking lenses.
In any case, I do think that we have to come to agreement
> as to what we are calling "ortho",I am not aware that "we" have come to an agreement as to what "we" are
calling 'ortho'.


> What, for example, should be the maximum image size (6x4.5, 6x6, 6x7,
> 6x9, even 6x12?), something else? IMO, a curious question. the maximum image size should be less than 6
x 7 , and certainly not the impossible to use, 6 x 9 or 6 x 12 size,
assuming the use of a standard MF viewer, which use commercially
available MF slide mounts.

> On Fri, Oct 14, 2011 at 8:03 AM, Bill G wrote:
> On 10/13/2011 11:31 PM, Don Lopp wrote:

> What does the width of the stereo image have to do with being an
'ortho' image ?
>Bill's answer-Nothing! Heck, this is stereo 101....Point of fact, the above assertion, regarding "ortho" and image width
was made on Oct 13, at 10:21 PM, PDT.

DON
Subject: Re: Ortho
Date: 2011-10-14 16:10:43
From: Bill G
On 10/14/2011 11:08 AM, JR wrote:
>
> I am glad that the subject heading has been simplified to the word "ortho". It appears
> to be the focal point of this discussion. (is that a pun?)
>
> Anyway, yes Don, it was me, not Bill who erroneously suggested the use of camera lenses
> for a viewer. In an offline letter, Don very correctly pointed out that the problem with
> that is viewing angle; that it would not be possible to see the entire slide (69mm was
> being quoted at that point) with that focal length (47mm or 50mm depending on whether it
> came from Don or Bill). (Thank you, Don),
>

Hi JR.... Seeing a 69mm wide slide with a 50mm loupe is possible, its 72 degrees HFOV....
its not commercially available....and if it was, it would suffer from distortion and off
axis coma a bit..... Unless you throw NASA type dollars at the design... Of course, the
straight-through viewing concept would have to dropped due to IPD.



> I did a test with a 50mm camera lens, and verified that what Don said was true. Then, I
got to thinking about why (aperture limitation in relation to back focal distance), and
why this "perfect" situation - same lens for viewing as acquiring the original image -
would not work.


There is "many" reasons a camera lens would never work as a viewing lens.... the design
criteria for the two optics are completely different, specially if you consider the eye
has to swivel.... so either one, or both of the optics would have to be greatly
compromised.... to the point of "why" ? The only thing that needs to match is the fl, and
it does not need to perfect match, as our brains have enough leeway in this area...


>
> It all got back to the concept of "ortho", that is, the same focal length for viewing as
> for shooting. And, the question that occurred to me is whether that is actually the case.
>
> Here is why it may not be: When you are shooting you are focusing the image on a
> photosensitive surface (this is the same whether you are using a digital sensor or
> film). That image is at a backfocal distance from the nodal point that is equal to (at
> infinity) or greater than the focal length (for anything closer to the camera than
> infinity). So much for optics 101.
>

Yep..... I like where you are going... :-)

>
> Now, if we just replace the photosensitive surface with the slide imaged by that
> surface, and look back though the same lens, we have the same focal length, and an
> "ortho" situation, right? Wrong. The "gotcha" here is that it is no longer the same
> focal length. Here is the reason: As soon as we look through the camera lens we are
> effectively changing its focal length, or to be more exact, the focal length of the
> entire "optical system".
>

A few issues....

First problem..... the ray pattern of a camera lens is completely different layout vs. a
loupe. For this reason alone, the entire concept is not feasible. You can not look through
a camera lens and swivel your eye to see the entire FOV....instead, you would have to
swivel your entire head around the camera lens. Just one glance of a the ray pattern of a
loupe should make this apparent.... Notice where the nodal point is on the loupe, its
outside the loupe, not between the elements... here is a 90 deg HFOV design of a 70mm
imaging circle....

http://i.pbase.com/o6/25/583725/1/100722550.O5HSr7uZ.SWAEPDesign.jpg

By looking through a camera lens, you don't change its fl.... the point you are inferring
though is a valid one... a change in magnification. But magnification is a relative term,
so it must always be compared to "something else".... and this is where things get
complicated in 3d viewing....

take a simple example, a typical near-far 3d scene. 10 ft to infinity. So in this
scenario, the magnification comparison would between what you see at the camera position
with your unaided vision, and what you see in the 3d viewer. If the tfl = vfl the size of
all the subjects projected onto the retina, in both the unaided and 3d viewing scenario
would be identical, so yes, its ortho.... the reason is, the same eye was being used in
both "optical chains" , so the eye fl cancels out. So all that remains is the fl of the
taking and viewing lens to achieve ortho (just ortho magnification here being addressed
here).

Where this can get complicated, is when you increase the fl of the taking lens, and
increase the near subject distance.... For a simple example, lets 2x the tfl. Using the
same scenario as above, the near subject will appear 2x larger on the retina in the 3d
viewing scenario, vs. what was experienced at the camera position with the unaided eye.
Simple enough..... BUT.... since there is no foreground in the scene to give us
near-distance perspective, the near subject will have the exact same retinal image size in
the 3d Viewer as compared to the unaided scenario, if you stood half way between the
camera and subject. And that is how we perceive it.... so in the 3d viewer, the near
subject will appear normal image scale, or ortho size.... but is the entire scene ortho?
NO! Because when viewing the distant mountains in the 3d viewer, they will appear 2x
larger compared to you standing half way between the camera and near subject. This is how
mismatching tfl and vfl will always give you distorted image scale vs. reality, or even
simulated reality (simulation of you moving close to the near subject)

So how important is this? It depends on the subject....if your brain has no reference of
image scale of a given subject, it will not seem unusual, its accepted. OTOH, if the
subject is of a known size, such as a car or a person, it can be noticeable.... this is
where our brains leeway comes into play.... at some point, as you keep increasing the tfl,
our brains will pick up on the disparity....


>
> There is another lens in addition to the camera lens, in between that lens and our own
> photosensitive surface, the retina of our eye. That is our eye lens. It would seem to
> me, that for a viewing system to be considered "ortho", you would have to include all
> optical elements, including our eye lens. This changes the effective focal length of the
> "system". It becomes a combination of the viewer lens plus the eye lens (and anything
> else in the light path, like the cornea, the eye fluid or vitrous humour, even the film
> of tear liquid or scleral fluid in front of the eye lens). Lets not even raise the point
> that the person doing the viewing may, or may not, also be wearing corrective
> eyeglasses. All of this, in addition to the viewer lens, combines for the actual focal
> length of what we "see" when we look into a viewer.
>

While all these points are valid.... i.e. variance in actual fl vs. nominal fl of tfl,
vfl, human eye, etc, in the big scheme of things, these variances are quite small vs.
doubling or tripling the fl of a taking lens... it comes down to the % of mismatch between
taking and viewing HFOV (which is a function of fl) There is ONE exception to this, and
that would a person that has huge refractive errors in his vision.... the corrective
eyewear has a much more profound effect when placed near a loupe, vs. viewing the real
world scene, so this could potentially create an artificial mismatch. However, the bulk of
refractive errors of the gen. population are within a few diopters, so luckily this was
never a major issue with the gen. population.


>
> In a previous comment, I raised the question as to whether the so-called "ortho"
> condition was really all that important (no one has answered this yet). In any case, I
> do think that we have to come to agreement as to what we are calling "ortho", and then
> move on as to a discussion of whether it really is necessary, followed by a very
> practical discussion of the optimal viewer design (actually, optimal compromise, which
> is what all optical designs are intended to be). In this discussion, we should consider
> all factors, physical as well as optical.
>

Are we designing a viewer here that I was not aware of? Or maybe this is just a
hypothetical viewer?.....

anyway, my take on this is as follows.....

There is two parts to ortho.... Z axis distortion, and image scale distortion. In this
case, I refer to distortion as a "variant from what a person would experience viewing the
scene with their unaided eye at the camera position - or some other defined postion". As I
mentioned above.... how important these two issues are revolve around two factors....how
great is the mismatch (i.e. does it fall within the brains leeway), and how "known" is the
subject matter, as the brain has tremendous reference recall.

As an example.... I have shot some crazy 3d scenes in the Redwood forests.... I had
experimented with many bases and fl's.... the scene was filled by objects, trees, rocks,
etc. Because I took the images, I knew what it should have looked like....but since the
people who viewed the images had never seen these forest, everything looked normal to
them.... they did not realize that boulder looked 3x larger, the far trees seemed waaaay
further in the viewer, etc. The near trees looked of normal size, but yet the far trees of
the same type looked larger (In the longer fl's images).... But no one would notice such
distortions, as they never experienced the scene, i.e. had no brain reference.

Where non-ortho becomes ultra obvious is with the things we have the strongest references
to, such as people, dogs, streets, cars, houses, etc. I have seen some real whacky
examples of this.... this is why I finally fell in love with fixed base stereo cameras....


>
> What, for example, should be the maximum image size (6x4.5, 6x6, 6x7, 6x9, even 6x12?),
> something else? Focal length (and perhaps more important, back focal distance),
> Immersion, accommodation for people who wear eye glasses, ambient light considerations
> (especially for eyeglass wearers, where light leaks in behind as well as in front of the
> glasses), and the myriad of other considerations.
>

JR, you ask all the right questions above.... and after 7 years of research and
prototyping, and learning optical principles that were not in writing any text, I can
answer all these in detail... but enough to fill a book. To keep this post from
bloating... my consensus is...

There is 3 avenues for film viewers...

35mm format... this the most cost effective system, both from the optics / viewer side,
and also the film. Its remarkable with the proper optics and duping techniques how good
35mm film viewing can be.... I considered bringing a design to market that would extend
the viewing to 24 x 43mm, so the image size would match the aspect ratio of modern 16:9
tv's. Of course, ideally, these would be captured on MF cameras and cropped down... If
3dtv did NOT come along, this IMO would have been a viable product, as the optics are
smaller and lighter, as well as the viewer... but it would still take a 5-6 element lenses
to accomplish this task.... I have prototyped this, and its superb.... a solid 55mm HFOV,
equal to cinema viewing experience, but with about 4x the resolution and about 5x the
brightness / contrast....is quite a treat on the retina....

MF size film.... Well, the big obstacle here becomes the size of the glass.... if you want
high resolution and wide HFOV, the lenses are massive, again, min. 5-6 elements, and in
the barrel, the size is equal to your clenched fist....this requires a very robust viewer,
robust adjustments, etc. Cost would be exorbitant.... to some, laughable.... just like
Leica Binocs at $4k, and those are high volume product compared to this viewer, so that
should put it in perspective....

Larger size films... say 4x6" and larger..... here you gain some cost savings in the
viewer and major savings in the optics.... about half the elements are required. The
reason is, as the back fl becomes greater, the amount of correction required becomes less,
and therefore less elements, and looser tolerances. This is why I called it the sweet spot
in a previous post.... but next you are confronted with the high cost of LF film.... and
the future availability of film, or the method to convert back to large film.... so the
next jump is to go all digital, and use darkroom printers to be assured a long term means
to convert images to a media that will be around. However, LED printers, to date, still
only print at 8 lp/mm, (and only one Durst prints at this high resolution, most are half
this rez)....therefore, you must produce very large images in the 16" - 20" range to keep
the resolution train fully optimized....granted this view is beyond superb, but its a
massive contraption that even hardcore enthusiasts would buck at.... its quite awkward
changing out 20" image pairs....

Then, move to a no optical system, such as the mIrscope... but presbyopia is my problem
with that system...and while we can wear corrective reading glasses....but this has
shortcomings as well, such as the spectacles are designed for correction in about 20 deg
on axis range, this limits the HFOV you can see properly corrected. In addition, the
distance from the center of the image to the spectacle is quite different than the edge to
the center, forcing the eye to accommodate IIRC about 1-2 diopters... some people do not
have this level of correction available in their natural vision....this is the value of
well designed optic, designed for a specific purpose..... it properly designed, it will
provide zero diopter correction when viewing the center of the image, or the corner of the
image....

Now, if you increase the image sizes any larger, you are nearing 3dtv sizes.....in which
case, it seems this is the most logical next progression in my mind....and this is coming
from a film lover... sad, huh....

So that is my short response to your query...would love to hear from others as well.....
and thx JR for starting useful postings such as this.... I am so tired of all the
"allegations" that are dead-end streets...

also thx for standing in the line-of-fire, explaining to Don, he mistakenly mentions I
write things that others write..... I know he gets confused, but it seems when others
mention these things, he accepts them.... when I state them, it just aggravates him even
more... I fully explained above why I would NEVER accept the concept of using taking
lenses and viewing lenses, but for some reason, Don still thought I have endorsed this
concept.... oh well..... some things are just can't be reasoned I guess.....

Bill







>
> Oh, and how about a new subject heading, like "The ideal medium format stereo viewer".
>
> Bill, Don, and all of you brilliant "lurkers" out there who could contribute ideas, what
> are your thoughts on this?
>
> JR
>
> On Fri, Oct 14, 2011 at 8:03 AM, Bill G <bglick@rconnects.com
> bglick@rconnects.com>> wrote:
>
>
>
> On 10/13/2011 11:31 PM, Don Lopp wrote:
> >
> > What does the width of the stereo image have to do with being an 'ortho'
> > image ? Just curious !
> >
>
> Nothing! Heck, this is stereo 101.... maybe this explains some of the massive
> confusion on
> the more complex topics?
>
> bill
>
>
> >
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>
>
> --
> stereoscope3d@gmail.com stereoscope3d@gmail.com>
>
>
>
Subject: Re: Ortho
Date: 2011-10-14 16:22:34
From: JR
The whole point of my comments was that the lengthy thread on "ortho" did not seem to come to any valuable conclusions, other than that it likely is unattainable in an MF viewer near the specifications mentioned.    I have not seen in the discussion any advantages in using "ortho" as a specification, which would imply restrictions or limits to any such design that do not appear to be necessary.   Therefore, it would seem to be time to move on to some of the other parameters that I suggested.

FWIW, I use the WESS 6 x 9 mounts.   These are single (monoscopic) frame-type black plastic mounts that I use as pairs side-by-side vertically in a Keystone Correct-Eye-Scope stereo transparency viewer, as well as individually in a pair of lantern slide projectors for polarized stereo projection.  Although I have not bought any for several months (I have some boxes of them on hand), I would presume they are still available commercially.

JR


On Fri, Oct 14, 2011 at 3:07 PM, Don Lopp <dlopp@rainier-web.com> wrote:
 

On 10/14/11 11:08 AM, JR wrote:
> I am glad that the subject heading has been simplified to the word
> "ortho". It appears to be the focal point of this discussion. (is
> that a pun?)

> Anyway, yes Don, it was me, not Bill who erroneously suggested the use
> of camera lenses for a viewer. I disagree as Bill did, IMO, take possession of your remark,
regarding the use of camera taking lenses as being suitable for use as
viewer lenses on Oct 12, 2011 at 1 PM PDT.


> It all got back to the concept of "ortho", that is, the same focal
> length for viewing as for shooting. And, the question that occurred to
> me is whether that is actually the case.
>
> Here is why it may not be: When you are shooting you are focusing the
> image on a photosensitive surface (this is the same whether you are
> using a digital sensor or film). That image is at a backfocal distance
> from the nodal point that is equal to (at infinity) or greater than the
> focal length (for anything closer to the camera than infinity). So
> much for optics 101. Which nodal point are you talking about ? Must we now measure focal
lengths to an accuracy of hundredths of a milimeter?

Apparently we are, now, parsing the word "ortho", into requiring
the measurement of the focal length of the viewer lenses. I can remember
being advised to always remember the word KISS, Keep It Simple, Stupid.

>
> Now, if we just replace the photosensitive surface with the slide imaged
> by that surface, and look back though the same lens, we have the same
> focal length, and an "ortho" situation, right? Wrong. The "gotcha"
> here is that it is no longer the same focal length. Here is the
> reason: As soon as we look through the camera lens we are effectively
> changing its focal length, or to be more exact, the focal length of the
> entire "optical system". Why and how are we able to look through the camera lens, especially if
it has a focal length of 47mm ?


It would seem to me, that for a viewing system to be considered "ortho",
you would have to include all optical elements, including our eye lens.

This changes the effective focal length of the "system". The system
does have a focal length ? How is it measured ?

It becomes a combination of the viewer lens plus the eye
> lens (and anything else in the light path, like the cornea, the eye
> fluid or vitrous humour, even the film of tear liquid or scleral fluid
> in front of the eye lens).News to me.


Lets not even raise the point that the
> person doing the viewing may, or may not, also be wearing corrective
> eyeglasses. All of this, in addition to the viewer lens, combines for
> the actual focal length of what we "see" when we look into a viewer.
In other words there are zillions of variables that must be taken in
to account before a determination as to what is an "ortho" condition.
(Don't forget the air temprerature). If this is the case, would "we" not
be better off if "we" we discontinued the use of the allegedly
un-defineable word "ortho".

THE question at hand was, "How is it possible to view a 3d image in
ortho, taken with a 47mm lens when the image is 69mm wide."

Will a Saturn MF viewer or a 3D World MF viewer provide an ortho view- I
don't think they will, as they both contain 75mm to 84mm focal length
viewing lenses, more than 50 percent longer than are the previously
described 47mm fl camera taking lenses.

In any case, I do think that we have to come to agreement
> as to what we are calling "ortho",I am not aware that "we" have come to an agreement as to what "we" are
calling 'ortho'.


> What, for example, should be the maximum image size (6x4.5, 6x6, 6x7,
> 6x9, even 6x12?), something else? IMO, a curious question. the maximum image size should be less than 6
x 7 , and certainly not the impossible to use, 6 x 9 or 6 x 12 size,
assuming the use of a standard MF viewer, which use commercially
available MF slide mounts.


> On Fri, Oct 14, 2011 at 8:03 AM, Bill G wrote:
> On 10/13/2011 11:31 PM, Don Lopp wrote:

> What does the width of the stereo image have to do with being an
'ortho' image ?
>Bill's answer-Nothing! Heck, this is stereo 101....Point of fact, the above assertion, regarding "ortho" and image width
was made on Oct 13, at 10:21 PM, PDT.

DON

Subject: Re: Ortho
Date: 2011-10-14 16:32:09
From: narjan@pipeline.com
JR wrote:

"FWIW, I use the WESS 6 x 9 mounts.   These are single (monoscopic) frame-type black plastic mounts that I use as pairs side-by-side vertically in a Keystone Correct-Eye-Scope stereo transparency viewer, as well as individually in a pair of lantern slide projectors for polarized stereo projection.  Although I have not bought any for several months (I have some boxes of them on hand), I would presume they are still available commercially."

AHA !

JR, let me throw a "dirty" question at you which (if we get distracted enough by it) might just pull us all out of this current
"Ortho" rut.

(Oh, "dirty" because this gets "bandied about" inconclusively every 3 to 5 years or so)

Here's the question :
Do you feel that the MF projection, especially of 6X9 slides, is noticably better than twin 35mm slide projection ?

Best Wishes,
John Billingham
Subject: Re: Ortho
Date: 2011-10-14 16:54:59
From: JR
Depends.   On a small screen, probably not.   But on a screen 4 or more meters wide (if you are not too far away), most certainly.    Details can be seen that otherwise would require a viewer.   The other advantage is the brightness potential.   The size of a 35mm aperture limits the amount of light you can put through it, no matter how bright the light.   With a lantern slide and a carbon arc like my Ampro Arc 20, you can really brighten things up.  Even Xenon lamps are not as bright as a white flame blown carbon arc.   The major problem is temperature.   For a still slide, I have to use a recirculating liquid cooled gate.   Even then, some of my slides have buckled from being left up too long.

JR


On Fri, Oct 14, 2011 at 3:32 PM, <narjan@pipeline.com> wrote:
 

JR wrote:

"FWIW, I use the WESS 6 x 9 mounts.   These are single (monoscopic) frame-type black plastic mounts that I use as pairs side-by-side vertically in a Keystone Correct-Eye-Scope stereo transparency viewer, as well as individually in a pair of lantern slide projectors for polarized stereo projection.  Although I have not bought any for several months (I have some boxes of them on hand), I would presume they are still available commercially."

AHA !

JR, let me throw a "dirty" question at you which (if we get distracted enough by it) might just pull us all out of this current
"Ortho" rut.

(Oh, "dirty" because this gets "bandied about" inconclusively every 3 to 5 years or so)

Here's the question :
Do you feel that the MF projection, especially of 6X9 slides, is noticably better than twin 35mm slide projection ?

Best Wishes,
John Billingham



--
stereoscope3d@gmail.com


Subject: Re: Ortho
Date: 2011-10-15 15:13:59
From: John Thurston
On 10/14/2011 10:08 AM, JR wrote:
> I am glad that the subject heading has been simplified to the word
> "ortho". It appears to be the focal point of this discussion. (is that a
> pun?)
- snip -
> In a previous comment, I raised the question as to whether the so-called
> "ortho" condition was really all that important (no one has answered this
> yet).

IMHO, the concept of "ortho" is over rated.

I think:
(A) It isn't really possible to capture, on two pieces of
film, all of the information required to recreate the scene.

(B) There is more at play than the focal lengths of the
taking and viewing lenses.

(C) I don't really strive for the recreation of the scene.

(D) The fact that I do not strive for this does not mean
others shouldn't try.
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us