Macrostereo Formula

[P3D Paul S. Boyer <boyer@xxxxxxxxxxxxx>]

John Bercovitz asks: "Did Kitrosser say anything about how _he_ came
to this formula?
I'm thinking w might be a stand-in for the usual focal length
used with a format times a constant.  Not sure what else is going
on here.  Would have to spend some time thinking about it.  Ouch!
8-)"

Samuel Kitrosser wrote the article "Polaroid Interocular Calculator"
published in May 1953 issue of Photographic Science and Technique,
Section B of the PSA Journal, pp. 74-76.  He gives a simple diagram
and the derivation of the formula used to make the interocular
calculator, which he designed.  In the early 1980s the calculator was
still available free from Polaroid in Cambridge, MA.  It is a
circular thing, but I found that it gives odd results which do not
agree with ordinary Realist-format practice.  So, as you say, I had
to do some thinking about it -- and ouch! was the result.  According
to my notes of the time, I found that the Polaroid Interocular
Calculator was based on a maximum deviation difference of about 1.2
prism-diopters, which is very modest.  McKay was recommending up to
2.5.  By examining the dimensions of the Realist intermediate and
close-up masks, and knowing the range of distances for which they
were recommended, I determined that Realist was using a deviation
difference of about 2.33.

The original Polaroid Interocular Calculator has three moveable dials
on a card.  Most of the measurements are in feet and inches, which is
messy, and had me so annoyed that I made a converted metric version.
I also added a setting on the inner dial which made things work out
right for Realist format.  It works, but to use it one must measure
distances, and know what the lens-to-film distance is.

So I find the M (magnification) method far simpler for macro and
near-macro shots.

Kitrosser's article begins: "The Interocular Calculator was designed
to provide a simple tool for correlating some of the geometrical
factors involved in stereoscopic photography.  The Interocular
Calculator has been used in the Polaroid Laboratory for about seven
years [it is marked copyright 1952] and several hundred are in the
hands of professional setereo photographers.  The following
discussion show how, with the help of the Interocular Calculator,
stereograms can be produced having maximum tri-dimensional effect
within the limits of comfortable viewing."

He concludes: "The Polaroid Interocular Calculator is of greatest
help to a photographer using a professional still or motion picture
stereo camera with variable interocular distance.  Having at his
disposal a choice of lenses of different focal lengths to suit his
artistic taste and the requirements of his subjects, he can use the
Calculator to determine the correct interocular distance."

Kitrosser in his acknowledgments thanked "especially Mr. William H.
Ryan, APSA, for his cooperation in developing the basic geometrical
theory ... "

--Paul S. Boyer   <boyer@xxxxxxxxxxxxx>


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