Re: Dukes' 12X VM viewer

[P3D john bercovitz <bercov@xxxxxxxxxxx>]

I saw John's viewer at the con.  The lenses are excellent:
no distortion and no color that I could detect.  The 
lenses are ~ortho for the 25 mm V-M personal camera.  I 
understand from John that the lenses are a major part of 
the cost and he can't control that part of it.
 
Remember that it is extremely difficult to get aberration-
free coverage and also full coverage of a "normal" angle 
view with ocular lenses of ordinary design if those lenses 
are of short focal length (short in an absolute sense).  A 
normal angle view has the focal length equal to the diagonal.  
Fortunately, the V-M format is fairly narrow having about a 
15 mm diagonal and approximately 25 mm lenses.  If this were 
not so, I think it would be _extremely_ expensive to make an 
ortho viewer as John has done.  As it is, because of the 
shortness of the lens, you can't have a lens of very large 
diameter and still be free of aberrations.  Consequently you 
can't make the lenses big enough to cover all IPDs.  An IPD 
adjustment would be good but with this short focal length, 
even a small adjustment of IPD would result in a wild change 
in convergence/divergence.  It would be so wild that you 
really couldn't handle it unless you can fuse pictures on 
opposite walls easily or things closer than your nose.  8-)  
In short, I think John has done the best that can possibly 
be done considering the limitations of optics this size and 
the depth of the afficionado's pocket.  
 
Same optical comments would apply to Hugo's viewer.  Hugo's 
viewer is a work of art.  It looks like an NC job to me.  It 
is not light in weight like John's which might be a problem 
but it didn't bother me.  It is for someone with pockets 
deeper yet.
 
In contrast, it is trivial to make a stereo system in medium 
format which is of normal angle and which is ortho.  There 
you would have 80 mm diagonal and 80 mm lenses.  Don Lopp 
showed me his home-built 47 mm medium format orthostereo viewer
at the con.  The angle was so wide I couldn't see all of the 
view (I wear glasses so I was backed off some).  I didn't see 
distortion or color in his viewer either but it was a bit hard 
to judge with the limited visibility.  I really don't know how 
he pulled it off.  Must be magic or a bargain with devil.  8-)
 
Ortho uber alles!
John B


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