Re: relation between squash and separation

[T3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

>> If I take a stereo pair with 200mm lenses and want to look at them in a
>> red button viewer.  can I increase the stereo-base when I take the picture
>> to counteract the squash effect?  I looked through past archives but
>> wasn't finding the answer to this particular question.

The quick answer is "no" because increasing the base affects all three
dimensions while increasing the mismatch between the taking and viewing
lenses affects only one dimension... John B. has written a lot on this
subject (I have made a few comments too) and it is all in past digests
(photo-3d digest).

>Whoops, a missing spec.  I have to go find it now.  From memory, the
>difference between the camera focal length and the projector/viewer
>focal length should be less than 20%.

When you way "projector focal length" you mean "effective focal length
depending on the viewer's sitting in the projector room", correct?

>Now this could be related to fatigue or eye strain, but maybe it does
>unsquash the image.  I don't know.

>I'm not sure if that would unsquash the image, but there is a simple way
>to find out.  If you manage to borrow etc. two virtually identical 200mm
>telephotos and take an stereo pair with one, then the two lens can be
>temporarily made into a viewer.

If you use the 200 mm lenses to take the picture and then 200 mm lenses to
view the image, then we are talking "orthostereo".  You will see a small
image with little depth (provided that you are only using 2 1/2 in. camera
separation) just as if you block most of the field of view when you are
looking directly at the subject.  If you increase the separation of the
lenses then you will see a hyperstereo...  The "squashing" is a result of
viewing the stereo image with much shorter lenses than the taking lenses.
I guess that's what you are suggesting, except the situation that we call
"squash" is a result of the taking/viewing combination and not built into
the pair during taking (as the "squash" suggests).

-- George Themelis


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End of TECH-3D Digest 135
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