[photo-3d] viewer optics

[Peter Abrahams <telscope@xxxxxxxxxx>]

>refer to "The world of 3-d; A practical guide to stereo photography" by
> Jac. G. Ferwerda.   Start with section 5.3 and follow any other secition
links.

   Supporting the idea that fixed eyepieces are OK, Ferwerda notes that
interocular distance is not necessarily identical to interpupillary
distance.  Lens separation should be equal to infinity separation on the
slides.
   Then he continues, 'though this is theoretically correct, the eccentric
viewing may give an unfavorable effect when the lenses are of a very simple
quality'.  
   My opinion is that the effect would very likely extend to other types of
lenses than 'very simple', especially when they are f2.
   However, even though I'm talking about the idea of adjustable
interocular, not any particular model;  I'm uncomfortable with the idea
that I'm sounding critical of a commercial product that I haven't tried.
------
At 04:59 PM 3/7/01 -0800, Peter Abrahams wrote:
>>I agree that the Red Button viewer uses mediocre optics [...]
>Excuse me?  Who said that?  Are you quoting someone Peter or is this your
personal opinion?
>Because I will have to respectfully disagree.

   Yes, I saw that coming.  
   We don't differ on one point: they are a 'joy to use'.
   The Red Button is the best viewer I've used.  But the eyepieces are, in
my opinion, something like 'mediocre' (noting that this means average,
neither good nor bad).   None of the problems I see are extreme, but given
that this is a 1950s product, a better lens was readily available.
   They shouldn't be compared with the other stereo viewers of the era that
use single element eyepieces -- those products were inexcusable -- doublet
lenses have been in common use since the 1700s.  Instead, we should compare
them with other types of eyepieces that were standard by the 1950s, in
binoculars, telescopes, and microscopes -- even inexpensive models.   These
were vastly better & show that the technology was available to produce a
much better product.
   The Red Buttons are quite sharp mid field, as any decent eyepiece since
the 1700s has been.  But away from the center of the image, they show
slight distortion (curved frame), astigmatism (fuzzy edges), and curvature
of the field (focus mid field, then to focus at edge of field you have to
turn knob)  to a degree that could have been inexpensively corrected in the
1950s.   Also, they were uncoated, at a time when most inexpensive optics
were routinely coated; and this makes a big difference in reducing
reflections off the eye lens and overall glare.
   They could also have been made with enough eye relief to allow for use
with spectacles, although very few binoculars were so made in the 1950s.
   I admit that much of the problem with the Red Button as used today, is
that we've adapted them to full frame use, and they were designed for
Realist format.  But the field curvature, for example, is apparent in
Realist format as well.
   Like I said, I enjoy my Red Button very much.  But I like my spectacles
as well, and my magnifying glass, and the windows in my house -- but if
each of these were replaced with a product that was well designed &
fabricated to optical standards, the experience would be much superior.  A
house window of optical quality would be extremely expensive, but a viewer
lens would be inexpensive.
   --Peter
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx   The history of the telescope & 
   the binocular:   http://www.europa.com/~telscope/binotele.htm

 

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