Re: Converging lenses (was: Window reversal); D|s-TortiO|\|s

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

>Hmmmmmm... okay you want a technical for-reality's-sake sort of reason for
>keystoning.
>
>I can think of one.  If my goal is to take stereo photographs which are
>intended to be viewed using the type of viewer commonly used for 
>"beamsplitter" stereo attachments, then keystoning would *improve* the
>technical reality-simulating result.

Way to go Mike!  You are a genious!

While talking about keystoning and resulting distortions, the assumption
is being made (but not stated) that a parallel viewing system is used.
This means either a viewer with parallel lenses or projection with 
parallel projecting lenses.  Of course, this is usually the case, BUT it 
does not have to be so.  

Using "beamsplitter" viewers or projection with converging lenses will 
cancel a similar keystoning in the taking lenses.

People tend to assume some kind of viewing arrangement when they talk
about how should the images be taken.  As an extreme situation consider
View-Magic prints, arranged one in the top of the other or slides taken
with with a Prism Beamsplitter (Delta, etc.).  Now try and view this with
a regular viewer (or freeviewing)!  Taking about vertical error! :-)  
Use a View-Magic or Delta viewer and... it works!  

Another example:  Use anamorphic lenses to take the pair.  Look at the
results with regular lenses.  Everything looks compressed.  Good if you 
are concerned about your physical appearance ("Weight watchers", etc.)
but not very realistic.  Project with reverse anamorphic lenses.  WOW!
Or, I should better say, W   O   W   !  !  !  !

Stereo photography is a two step process:  

Step No. 1:  Take the picture.
Step No. 2:  View the picture.

You cannot comment on Step 1, without taking Step 2 into account.

Sorry folks for this lecture, but my email ID comes from Case Western
Reserve University...., an institute of high learning. Ha, ha, ha!
I love photo-3d!!!

                                            -- George Themelis :-)

PS.  Thanks Mike!  I was hard-pressed to find a reason for taking
pictures with keystoning... Now I know a very good one.


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