Gabriel's puzzle!

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

Thanks Gabriel for an interesting puzzle!  I was aware that the direction
of movement dictates whether you will get a straight (parallel) or crossed
pair, but now I know why!

First, I made a mistake earlier when I said that you should first take the
right picture and then the left (in single SLR pairs) if you want to
freeview the roll.  I think it is the other way around.  The left picture
will be at the beginning of the film (left side) and should be viewed with
the left eye.  In regular stereo cameras the first picture is taken by the
right lens hence the pairs are reversed.

Now, assume you are in a airplane.  You have the option to seat either in
the left slide or the right side (facing forward).  Here is a diagram of
the situation:

                          
Left side observer:       (1) L             (2) R
                           \                 \
  Airplane:            >----X---->       >----X---->
                           /                 /
Right side observer:      (1) R             (2) L


It is clear that the observer in the left side will take the left picture
first, while the observer in the right side will take the right picture
first (you might have to turn your head 180 degrees to see that!)

The results are summarized in the following table:

Situation        For the pair to be freeviewed you must:
--------------   ---------------------------------------------
Single SLR       Take the left picture first
Moving vehicle   Be in the left side of the vehicle
Moving subject   Subject must be moving from right to left

Regards -- George Themelis


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