P3D optics of stereo viewers

[Peter Abrahams <telscope@xxxxxxxxxx>]

I acquire Red Buttons because they're the best available viewers for stereo
slides.  If you open up the slide carrier windows, you can see 7 perf, but
anywhere near the edge they are not at all sharp.   They are sharp enough
in the middle of the field and become blurry near the edge.....not right at
the edge, but maybe 2/3 of the way to the edge.  This is nowhere near as
good as could be, a flat field magnifier (such as a high quality loupe used
to magnify negatives) would give vastly better performance.
I haven't spent the time to determine whether the doublets in the RB suffer
from astigmatism, coma, or field curvature, (likely the last).  I haven't
checked out their color correction or contrast.  They are pretty decent
lenses, but a viewer with the best available lenses (commercially
available, not research optics; and maybe even spherical without getting
into aspheric optics) could be far better.   I don't know if I'd be willing
to pay for a viewer such as this, but a 'hacker' could easily rig one up
with a RB or other viewer, replaced with some optimized lenses of the
correct focal length.

Jon has said that he will be offering the Hugo de Wijs (spelling???  memory
in general???) viewers.  These were on display at NSA Bellevue, and were
beautifully machined & used optics that were better than anything I had
seen in a stereo viewer; and were extremely expensive.  It really is
important to get good optics out there, for until you've seen the best, you
don't know what you're missing.

>I've got several viewers whose apertures cover 7+ perf with decent
>internal illumination and achromatic lenses... optically they are not NEARLY
>the equal of the camera glass and do not cover the field.
>Sorry, but the Red Buttons DO NOT cover 7 perf, and typically have
>marginal contrast (haze). Kodaslide IIs and Reveres better on contrast
>but no improvement in coverage. Wollensaks seem to have best wide
>coverage, but do it with less mag/longer fl. And how about people with
>different eye corrections, which is exceedingly common?
>..... I'm looking forward to what Jon Golden will be offering in
>the next few weeks; from what he's told me there'll likely be some
>relief there.

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AND.....re: antiquing brass. using ammonia is indeed the quick & dirty
method.  I haven't done the fuming method, but painting it onto clean brass
will give a streaked browning that worked fine for me.
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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