P3D RRe: sharp viewing lenses

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

>>There must be a reason that no commercial viewer has been produced 
>>yet with such (flat field) lenses.  

>Hmmm, I think you know the answer to that one without realizing it. :-)
>As people put more emphasis on the camera and scant little on the viewer
>(in general), the same goes for manufacturers. 

Yes, I do know *that part* of the answer... But I suspect there is more to
it.  First, there is the law of "diminishing returns".  How much
improvement do you get for your money? (Same law applies for camera
optics... How much better is a Realist 2.8 compared to a Realist 3.5?)  
Second, there is question of how well the better optics work.  Realist made
a so-called "Gold button" viewer that uses 3-element lenses of a shorter
focal length.  The performance of these lenses is, IMO, disappointing. 
They do not even cover 5p.  Some people (especially those wearing glasses)
even prefer the single-element lenses (of, say, a Brumberger) because they
have better coverage.  So, how well are 3- or more element-lenses going to
work in a viewer?

>What was the price
>ratio of the 50's 3-D cameras vs. the viewers (rhetorical question)?

The ratio was 1:8 for the Realist 3.5 (camera $160, viewer $20).  People
expect that the mechanically complicated camera should cost more than the
simple viewer.  Today you can still get a Realist for $125 so people
naturally hesitate to spend that much or more for a viewer.  Realizing that
the expense of good viewers might be slowing sales, 3d equipment
manufacturers produced cheaper versions of viewers (examples: red button
vs. white button for Realist and Kodaslide II vs. Kodaslide I for Kodak)
and sales must have been good, judging from the number of KI's and
Brumbergers around.

>Are camera optics more complicated (or expensive) than viewer optics?

3 and 4-element lenses in stereo cameras are more complicated than
2-element achromats in viewers but the viewer lenses are considerable
larger than the camera lenses.

>In regards to 7p, how was this width chosen? Does this have to do with
>the associated loss of image from the camera lens displacement?  

The Realist is very clever format that manages to achieve constant 10
sprocket film advance, reasonable interocular distance (even though in the
wide side) and minimum loss of film (frames are almost touching each other
with overlaps being a common problem amount Realist-format stereo cameras).
 
In the Realist format there are 3 frames between the lenses.  If you want
to go wider then you are looking at two frames between the lenses and two
film sequence advances.  7p size will give you a reasonably small
interocular spacing.  Full frame pairs can be used in this sequence but the
result is again enlarged interocular (I think some RBT cameras use this
format).

7p must have been seen as a reasonable choice for a camera with a 65 mm
lens' spacing and was chosen by some European cameras (Iloca, Belplasca,
Verascope) but it never became popular... Even Iloca replaced their 7p
camera with 5p cameras after Realist became the standard stereo format of
the 50s.

-- George Themelis


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