[Atmswap] 13.5" Diameter F # 2.4 Schmidt System Available

[Sidor . Kurt]

Dear List,

This is a long message with many pictures of a rare item for sale.  If you
know of anybody who may be interested in a large, rare, and unusual Schmidt
system please forward this message to them, I know only a limited number of
ATM List members also get the SWAPLIST.

Thanks!

Kurt Sidor



Found: One Large Schmidt Collimator, It is now for sale.

What is a collimator?  Is it simply a telescope system used in reverse, put
an illuminated source at the focal point and project it out of the full
aperture as parallel rays.  Used in optical bench work for alligning other
instruments or even used as an artificial "star".  

Summary: It is a 13.5" clear aperture, 31.75" ish focal length, F# 2.4 ish
Schmidt system.  The corrector has all its Schmidt curve polished into the
front surface only, the rear surface is flat.  The primary mirror is 16"
dia, ROC 63.5" and its curvature is ELLIPTICAL!!  Technically its actually a
Wright type Schmidt system (which it better suited for this configuration,
the corrector is placed at the focal length rather than the ROC.)  If you
are not familiar with the Wright system look in "Telescope Optics Evaluation
and Design", they have a good write up on this variation of the Schmidt
system.  And unlike the Schmidt-Newtonian with a spherical primary this one
is elliptical matched to a stronger Schmidt plate)  The biggest advantage of
the Wright design Schmidt system is that it produces a FLAT image plane.

Here is the nameplate that was on the outer shroud:

http://images.andale.com/f2/115/106/3663062/1016202256079_nameplate.JPG

Here is the tube, length 32"

http://images.andale.com/f2/115/106/3663062/1016202309352_tube2.JPG


Here is the tube again, welded and machined aluminum

http://images.andale.com/f2/115/106/3663062/1016202304566_tube1.JPG


Here is the Schmidt plate as it was found, the central obstruction is 2.25"
dia.  Note the lenses inside and the "peep-hole".  At one time this peep
hole held a 45° mirror, which is no longer there.  This is how the light got
into the focal point from an illumintor assembly attached to the outer rim
of the tube.  The focal point and grating or pinhole would have been
attached to the other end of the tube just at the inner surface of the
Schmidt plate.

http://images.andale.com/f2/115/106/3663062/1016202293263_schmidtplate.JPG

Here it is after I cleaned it, just good enough for checking against optical
flats, it has a few small scratches but really is still very good
(especially considering how I found it):

http://images.andale.com/f2/115/106/3663062/1016202298551_schmidtplate2.JPG


Here is the outer "illuminator" assembly I described above.  it has a few
lenses in it but no lamp anymore, some pieces are missing:

http://images.andale.com/f2/115/106/3663062/1016202245613_illuminator.JPG

Here is the front surface of the Schmidt plate being checked with a 4" flat.
Note the neutral zone is located at 3 5/8 inches on my ruler.  The ruler is
butted up against the central obstruction tube of 2.25" dia or 1.125"
radius.  3.625+1.125 = 4.75" radius for the neutral zone.  Divide this by
the clear aperture radius of 6.75 puts the neutral zone at 4.75/6.75=0.704.
Clearly the neutral zone was polished in around the 70.7 % zone.   The
corrector plate is about 1.0" thick.

http://images.andale.com/f2/115/106/3663062/1016202260660_neutralzone.JPG

Here is a closeup of the fringes, note how many there are, this is clearly a
deep, strong Schmidt plate.

http://images.andale.com/f2/115/106/3663062/1016202266154_neutralzonecloseup

Here are fringe veiws at various locations around the front surface, roughly
every 120°

http://images.andale.com/f2/115/106/3663062/1016202276441_schmidtcurve1.JPG

http://images.andale.com/f2/115/106/3663062/1016202281650_schmidtcurve2.JPG

http://images.andale.com/f2/115/106/3663062/1016202287357_schmidtcurve3.JPG

Here are fringe views of the internal surface of the Schmidt plate.  Note
they are flat, not optical surface "mirror" tenth wave or better flat, but
definately a quality flat surface for a large refracting window.  The images
are taken roughly every 90° or so.

http://images.andale.com/f2/115/106/3663062/1016202222818_flatside1.JPG

http://images.andale.com/f2/115/106/3663062/1016202228207_flatside2.JPG

http://images.andale.com/f2/115/106/3663062/1016202234279_flatside3.JPG

http://images.andale.com/f2/115/106/3663062/1016202239988_flatside4.JPG

Here is the mirror, 16" dia, ROC 63.5".  The coating is old but the surface
itself is not damaged.  The mirror is about 2.5 to 3" thick.

http://images.andale.com/f2/115/106/3663062/1016202250895_mirror.JPG

Here is a Ronchi image of the primary mirror, you can see the damaged
aluminum coating but you can also see that the figure in the damaged areas
are still good.  This image was taken with a 2.5 LPMM sinusoidal "Ronchi"
grating, a 0.005" wide slit source with a 650 nM LED, a Vivitar 28 MM Nikon
mount camera lens, coupled to a Sony B+W C-mount CCD video camera with a
SNAPPY.  The tester and grating were located approx 0.75" inside of COC.
Note that the fringes bow outwards unlike those of a parabolic under the
same test inside of COC.

http://images.andale.com/f2/115/106/3663062/1016543884708_schmidt1.JPG

Here is a comparative RONWIN ronchi simulation produced under similar setup
parameters.  I then varied the conic constant to approximate the mirrors
elliptical curvature, constant K=0.4 is a close fit.  This is just an
approximation, not a firm number for reverse-engineering this system.  Thank
you John D. Upton for making this shareware available.

http://images.andale.com/f2/115/106/3663062/1016543878778_ronwinschmidt.jpg

Also here is the outer case for the whole tube assembly:

http://images.andale.com/f2/115/106/3663062/1016202271748_outercase.JPG

I know it looks rough but the whole thing is there as far as the "telescope"
is concerned and appears to have been built to a very high quality level
(30+ years ago).

Let me know what you think.  This is a rare find.  Compact tube, fast
optics, aperture...that cental hole and tube assembly is just screaming for
a nice CCD camera!!!!  The biggest advantage of the Wright design Schmidt
system is that it produces a FLAT image plane.

If you are having trouble visualizing the complete instrument, I will
probably be reassembling it shortly and make a photo avaialble.  Although I
personally think that shipping it in separate pieces is probably a safer
idea.

Serious offers being considered.  If I get no real interest its off to EBAY.

Thanks!

Kurt Sidor
Mechanical Engineer
Dynamics Research Corp.
Encoder Division