[photo-3d] Re: Quiz: Movement of clouds/direction of shoot

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Follow those clouds!

In a stereo scene the nearer an object is to infinity, the *less* it
appears to move in our field of view between left and right images - while
closer objects show *more* sideways displacement in our field of view, as
we move from one vantage to the other.  You see this when the moon
"follows" you while you're driving at night - it remains steadfastly in
the same place in your field of vision, while nearer objects shift
sideways with different speeds, depending on how far they are.  That's how
stereo works - near things show large parallax, distant things show
little, infinitely distant things show none.

Assuming those clouds are the most distant objects in your scene, they
should act like the moon between shots and stay in practically the same
place in the left and right views.  If those sneaky puff balls are moving
during a sequential stereo shoot, you must follow their movement to keep
them in the same spot in your viewfinder, or as nearly so as possible. 
This forces them to appear at infinity, or farther than anything else in
the scene.  If you shoot the other way around, the clouds will occupy very
different horizontal positions in the two views and be interpreted by your
brain as near objects - and that is an effect you are not usually striving
for.

OK, so I don't win for brevity.

Bruce

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