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On 07/04/07, Parker Dinkins wrote:

> on 4/6/07 6:40 PM US/Central, George Brock-Nannestad at
> [log in to unmask] wrote:
> 
>> There are several factors involved in good stereoscopy. First of all,
>> each image must obey the rules of perspective, which means that the
>> angle subtended by an object must be close to the natural angle of
>> observation. For an ordinary telephoto image that means that you must
>> see it from such a long distance that you really do not draw it
>> closer, and a wide-angle image must be seen with an eye so close to
>> the image plane that you may not be able to focus and hence you need
>> to use a lens - usually called a magnifier. All of this makes for
>> some simple geometrical calculations.
> 
> While I'm sure this is especially true for stereo images, isn't this
> also true for other images?

Yes. Leonardo da Vinci discusses this problem.

However, people nowadays have all learnt how to remap perspective images
that are viewed from the wrong position. Otherwise there would be only
one acceptable seat in the living room for watching TV. Likewise in the
cinema.

> 
> I recall calculating many years ago that the most accurate perspective
> for enlargements made from 35mm negatives and slides, when held by
> hand at a normal viewing distance, was achieved with lens focal
> lengths of 35mm for enlargements made at 8"x10" and 28mm for
> enlargements made at 11"x14", respectively. I rounded these figures to
> readily available lens focal lengths and print sizes.

It is true that if you get the angle of view right, and shut one eye, a
flat perspective image can look surprisingly real.

Regards
-- 
Don Cox
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