Re: Twin 35mm Stereo setups info wanted

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

Linda Sherman/Ralph Johnston wrote:

> All this is to get some kitten photos on the internet in 3D!

Sam Smith wrote:

> kitty shots at a short distance require a lot shorter stereo base than 
> you could get through twinning. 

What sort of stereo are you going to put on the web?  Anaglyph, pairs, ?
Just curious.

One thing about computers, you view the pairs from a ways back.  This 
calls for a longer lens than usual or, you can crop and magnify the 
image to get the same "viewability".  (It's also the same distance from
the camera to the kitten and hence the same perspective.)

Let's say you're going to make a 75 mm (3") wide cross-eyed pair.  Let's
say you have a couple of 35 mm point n shoots which you are going to join 
bottom to bottom in order to reduce the stereobase to a minimum.  Let's
say your audience will view the 75 mm-wide pair at a distance of 500 mm
(19 11/16 inches) from the screen.  How much of the negative can you use?
(Gratuitous info: The negative will be 24 mm wide and 35 or 36 mm tall 
because of the way you join the cameras.)  The width you can use is:

         35
    w = ----- x 75 = 5.25 mm or 13/64"
         500

5,25 mm is about 1/5 of your frame width so make sure the kitties stay
within 1/5 of the frame width when you shoot or you will have distorted
cats.  Distorted cats suffer much more than Schroedinger's cats.

Don't worry about losing resolution because of using so little negative.
Computers don't have any resolution to start with.  8-)  Just kidding but
in this case it's true.  Well, let's see if it's true; I could be lying.
75 mm at 72 dpi is about 210 pixels.  Film ought to do about 40 lines per
mm if the camera has a lens 8-).  So 5.25 mm * 40 lpmm = 210 pixels.  Wow!
talk about a coincidence.  That and how close I came to lying!  8-)

I don't know how old the kitten is or if you're taking him in profile or 
head on.  Let's say profile and he's 160 mm wide as he sits.  Then you have 
to back off to a distance of 1070 mm (42") to make him fit in the allotted 
space on the film.

                  160
     distance = ------- *  35 = 1070 mm
                  5.25

As far as getting the stereobase small enough, it will probably be about
right if you use point n shoots joined bottom to bottom.  Your kittens will
appear slightly oversize in the result but not noticeably.  Or you could
sell them as Ragdoll or Maine Coon, right?  8-)

John B


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