T3D custom lenses for viewers

[Peter Abrahams <telscope@xxxxxxxxxx>]

Custom designing lenses for a viewer is a great idea, but I see too many
difficulties to be optimitic.  Some random thoughts:
--I'd hesitate to make the lenses large diameter to accomodate IPDs.  I
think that viewing through anything but the center of the lens will produce
aberrations and limit eye relief.  As far as I know, you need to view
on-axis in any normal eyepiece.  My eyes are 57mm apart, and many people
are in the 70s, so a compromise covering the 60s wouldn't work for many.
Make them large diameter to cover the whole field and allow for movement of
the viewer in the hands.
Viewers for stereo prints don't have IPD adjustments but are cut from
lenses of relatively huge diameters.
--A designer can tell you with certainty that 'this lens will work to these
specifications', without making one for you.  But until you look through a
lens of those specs, it's tough to say that the lens will make you happy,
especially regarding the significant costs.  As has been discussed, stereo
can enhance the effect or visibility of some aberrations that are
insignificant in quality lenses under normal use.  So, there will be a
gamble. There are so many factors to an image that aren't part of the
primary design of 'field of view - free from aberrations'; including color
fidelity, glare from light off the edges of the lens, contrast loss from a
polished surface that isn't perfect..... on & on.
--If the highest quality loupes for viewing negatives are the proper focal
length, I doubt that a custom designed lens would greatly improve the
performance over them.
--The price for these lenses almost certainly wouldn't include a cell or
mounting device.  (the individually focusing cell mentioned in the loupes
would be a big plus, many people have mismatched eyes.)  Fabricating a
viewer is a very difficult project, if you're going to include IPD and
focus adjustments.  And I really doubt that we could sell 250, or even 100.
 Making them the size to fit red buttons would help sell them, but that's
pretty small diameter, I'd guess it would compromise performance.
--I think we'd want 35mm, 7 perf, but I don't think there's enough
consistency in cameras we use to make 'ortho' anything but an arbitrary
compromise.

I'd very much like to see such a lens, since a really optimized system of
modern design and modern manufacture will almost always give greatly
improved performance.  It doesn't sound workable to me, though.

I hope we get lots of reports from the conference, I'm sure there's no end
of interesting talks & displays.
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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