Depth, how much is too much?

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

How much depth is "enough depth"?

This is an interesting question with technical and aesthetical implications
that cover all aspects of stereoscopic imaging from recording to viewing.

There is a quantity that measures depth.  It is the maximum deviation. 
This is the difference in separation of the closest and furthest points of
the scene.  It is recommended that maximum on-film deviation is limited to
1.2 mm in 35 mm slides.  This is how much deviation exists in a scene with
objects from 7 ft. to infinity shot with a Realist and approximately
obtained when following the 1/30 rule.  This is just a recommendation.  For
various aesthetic (or technical) reasons one might want to introduce less
or more.

Aesthetically, there is no reason to have this maximum amount in every darn
stereo slide.  I recommend the conservative approach "less is better".  I
am willing to bet that the particular slide that won first place in Detroit
had more than the maximum recommended on-film deviation.  Considerably
more.  As I said, I felt my eyes hurting when scanning the scene from front
to back.  

Now, that was a picture of a book (Bible) on a table, a pair of glasses at
the top and a background limiting the depth.  While you could put the
maximum deviation in this scene, aesthetic reasons question this practice
for a picture where mood and effective composition and lighting are the
main elements.

Since the picture was shot with an SLR camera in a slide bar, the maker had
the option to introduce as much depth as he liked by controlling th
translation between the two shots.  I found the depth more than enough. 
Obviously, the maker and other club members (including Mr. Seymore Depthe)
did not think so.  I would like to see this picture projected in the next
meeting and have the club comment on it.

Viewing is an important factor too.  The most difficult situation is in
projection, especially large screen projection, where less depth is
recommended.  Mike and I were sitting in the last row which is the worse in
terms of emphasizing the depth ("stretch").  In a viewer this picture might
have been better for me.  Computer displays require more depth for
effective stereo effect, IMO.

Yours in Depth, George Themelis

PS.  Regarding the hidden message stereopsis test that Paul asked about, I
made one some years ago.  Anyone can make their own by shifting random
letters to read a message.  A computer and B&W printer (or even a
typewriter!!!) is all that is needed (just ask Gabriel if you have any
questions or want or want to get fancy!)  I consider this a demanding test.
Anyone who can read the message must have healthy stereopsis.  I have only
found one erson who cannot read it.  It would be interesting to time the
responses (time required to see the message).  My contribution is to have
this in a standared stereo format slide and use a Realist viewer, which is,
IMO, the easiest way to see 3d.


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