P3D Clueless Teri

[George Themelis <gthemelis@xxxxxxxxx>]

Dear Teri,

You appear to be very interested in stereo photography and eager
to learn and participate in our discussions.  You are asking
what orthostereo means.  I came up with a short "tutorial" that
might be of interest to you and other beginners in this list. 
Please feel free to ask any questions after I am done lecturing
:-).

We must start with the simple fact that we have TWO eyes, spaced
about 2.5 inches in our heads.  Stereo photography attempts to
reproduce the effect of seeing with TWO eyes.  Therefore it
requires TWO pictures, the LEFT picture and the RIGHT picture. 
When the left eye sees the left picture and the right eye sees
the right picture then the result is DEPTH!!!  

This is a miracle of nature and we get to reproduce it every
time we take a stereo picture.  Sometimes we wonder why doesn't
every one do the same.  There are some inherent difficulties as
you will see shortly.  But still the effect is so amazing that
many of us still wondered why is this such a well-kept secret
and do our best to initiate others (like yourself).

Now, it is important to realize that the two pictures seen by
the eyes are *not* identical.  There are small difference and it
is these differences that result in the sense of depth.  If you
make double prints and make the left eye look at one of the
prints and the right eye see the other (identical) print, then
the result will be FLAT as a pancake.  No differences, no depth!

Where do these differences come from?  Our eyes are displaced by
roughly 2.5 inches in our heads.  This displacement is
responsible for the small differences in the two views. 
(Experiment: Extend your finger in front of your eyes and
alternate each eye.  Notice how the finger "jumps" with respect
to the background.  That's evidence that each eye sees a
different picture.)

The simplest way to record a stereo picture would be to take one
picture at eye level and then shift the camera by 2.5 inches
(just like our eyes) and take a second one.  What you have just
done is to record a STEREO PAIR.  Simple, isn't it?

So far, so good.  But you need somehow to bring the left picture
to be seen by the left eye ONLY and the right picture to be seen
by the right eye only.  How can you do that?  This is what makes
stereo photography more difficult than ordinary photography. 
You see, unlike our ears, our eyes are well coordinated and
inflexible in certain movements.  They cannot move up and down
independently.  The issue of ALIGNMENT is important in stereo
photography.

So, put the two pictures down, next to each other, side by side,
carefully aligned vertically and separated by 2 inches or so (no
more than the spacing of your eyes, less would be easier to
handle).  There are viewers that will help each eye focus on
each picture.  It might take some practice.  Imagine, there are
people (yours truly too) who can diverge their eyes and direct
them to each picture, and see stereo WITHOUT using any viewer!!!
 This is called (parallel) "freeviewing".  Others will place the
left picture in the right side and the right picture in the left
side and then CROSS their eyes (so the right eye sees the right
picture, etc.).  This is cross-eye (free)viewing.

For a beginner like yourself freeviewing might be a frustrating
exercise so stick with the viewers.  There are viewers in the
market for prints, slides, etc.  Plus, viewers that let you put
your two prints one at the top of each other (instead of next to
each other) and then direct your vision up and down.  Not to
mention anaglyph (one image is colored red, the other blue and
you wear red/blue glasses so that your "red" eye sees the blue
image) or polarized projection.

All these viewing methods have one goal:  To make your left eye
see the left picture and the right eye see the right picture. 
That's how you get the "stereo effect".

If it was not for the viewing problem and the resulting
limitations in size, need for viewers or glasses, etc, stereo
photography would be much  more popular than it is today.

But don't let that stop you!!!  Record a stereo picture as I
suggested.  Use a viewer to view it.  You might be very pleased
by the stereo effect and become a lifelong stereo enthusiasts
like many of us!

To be continued.... stay tuned!  Lunch break... Pizza is here!
:)

George Themelis



=====
George Themelis (DrT-3d@xxxxxxxxxxxxxxxx)
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