P3D Dear Teri - Part III

[George Themelis <gthemelis@xxxxxxxxx>]

Dear Teri,

I hope you are still with me.  So, you shifted your digital
camera by about 2.5 inches or 65mm for the rest of the world
(more or less, don't worry if it is not exactly 2.5 inches),
duplicating what the eyes see.  Great!

In stereo photography you can use ANY trick has ever been used
for 2D photography, PLUS you have an extra control that you
don't have in 2D.  This is the amount of shift.  For starters I
recommended shifting the camera by 2.5 inches, which is the
spacing of the eyes.  You are then recording ORTHO stereo.  But
you can also shift 30 feet or 1/10 inch if you like.  Why would
you consider anything else than 2.5 inches?

First, consider the case of photographing distant objects.  Our
stereo vision drops off quickly as things move away from us. 
The clouds and distant mountains have no depth because they are
so far away.  You must have noticed when you use binoculars to
view far away objects, they look rather flat.  That's because
they are far away.  If you only shift your camera by 2.5 inches
then the two pictures of far away objects will be practically
identical and your brain will see no depth in this pair.  You
can put more depth in a far away scene by increasing this amount
of shift.  Then you are recording what is called HYPER-stereo.

The opposite situation is when you photograph close-by objects,
like a close-up of a flower.  Because this is so close to you,
you will normally need less than 2.5 inches of shift.  You will
then be recording a HYPO-stereo.

Think of it this way:  Your point of reference is 2.5 inches. 
This is ORTHO.  HYPER means MORE, HYPO means LESS.  So HYPER is
more shift and more depth, HYPO is less shift and less depth.  I
know Larry does not like these terms but for me they are just
fine (especially since they are all derived from Greek, I feel
like home!)

Now, here comes the natural question:  If you decide to go for a
hyper or hypo, how much should you shift the camera?  For
starters, follow the 1/30 guideline which says that the shift
should be equal to 1/30 the distance of the nearest to the
camera object.

But there is A LOT you can do by just shifting 2.5 inches EVERY
TIME!  If the mountains are far away, you can frame them with
the nearby trees or bushes.  Shoot ortho until you are tired of
it (and this can take some time) and you feel like experimenting
with something else.  

So, now you know what ORTHO, HYPER and HYPO means.  Is there
anything else in stereo photography?

Sure, there is more!  But this good enough for starters.

I will wrap things up in my next posting.

George Themelis



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George Themelis (DrT-3d@xxxxxxxxxxxxxxxx)
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