P3D Matched lenses in stereo

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Recently there has been a discussion in New.3D.Film.Gear@xxxxxxxxxxxxx
list regarding the tolerances in matching lens focal length (or image 
size) of R and L lenses.  No one seems to have a clear answer of what
this size tolerance should be.  Ferwerda mentions 1% somewhere 
but only indirectly.  Michael Kaplan suggested using 2x2 projection
with zoom lenses of identical slides and vary the FL of one slide
to see at which point the difference in size becomes noticeable and/or
bothersome.  Then I suggested that we ask camera manufacturers (from 
Realist to RBT) about their tolerances in matching lenses.  Michael 
then asked:

>I just looked at 5 of my stereo cameras and only the TDC Vivid uses the
>word *matched* on the lens mount. Are there any other vintage cameras
>that state their lenses are 'matched'?

And I reply:

I am sure every decent stereo camera manufacturer put a lot of effort in 
testing and matching lenses.  Most mention "matched lenses" in their 
literature even if they do not put it in the lens barrel... 

Ed Romney in his "Realist repair" book recalls a conversation with a 
"Mr, West" in the '70s who was around and remembered how Realist ordered 
batches of Ilex Paragon lenses, tested them all, selected the best and 
matched them individually for focal length.  Many were sent back, he 
remembers.

Also, from pencil markings in the barrel of Kodaslide II viewer lenses
it is clear that Kodak was even matching viewer lenses!

On the same subject, Ed Romney writes: "On the necessity for matched
lenses in stereo.  It is not as important to have lenses of identical
focal length as many people believe.  The eye has great powers of 
accommodation.  My left eye has 1 diopter higher prescription for glasses
than my right eye, yet I see stereo.  You realize that for me both images
are not the same size.  35mm lenses off the self will agree by 1mm as a
rule which is about 3%.".  He then explains how to adjust the focal
length of any Tessar (4 element) or Triplet lens by moving the front
element.  Later, he says that when he mentioned to Mr. West that he
found remarkable ho much the eye could accommodate for framing errors,
different image sizes, imperfect focus in one eye, etc. and still
see stereo, apparently Mr. West told him to back off :-)  He used the
term "eye bombardment" to categorize interference that reduces the
stereo effect.  It does not PREVENT stereo but give eyestrain 
particularly after several slides have been viewed, stereo is
not pleasant, it is not enjoyable.  "STEREO HAS TO BE REALLY GOOD
TECHNICALLY TO PLEASE, he emphasized."

George Themelis