ATM Tinsley Cass./Class or DK. Off topic....

[Bill & Tracy Marriott <btk@pacbell.net>]

This is slightly off topic for the ATM list, but interesting, especially 
with all the noise recently....<G> Also posted to sci.astro.amateur, 
which may be more appropriate..



When I acquired this 12" Cassagrain made by Clayton Tinsley, supposedly 
in 1929, it was thought that it was a classical Cassagrain, presumably 
based on its 67 years…

When I first got the optics home, I put the primary on the test stand, 
and, for a f3.8 , looks fairly under corrected.

Now, in an article written by David Levy, who used to own this scope, 
for the Mt. Wilson Observatory Association, he mentioned that the 
astronomers on the mountain during the 30’s noted that the optics 
weren’t perfect, but they were good enough for use at the visitor’s 
Hotel, where this telescope was set up.

As I am getting ready to put the OTA back together, I figured its time 
to figure out what I want to do about the optics, either just get them 
recoated, or possibly rework the optics, in general they’re in fairly 
good shape, but both primary and secondary have their share of 
scratches.

The question is, what defect were the astronomers on Mt. Wilson talking 
about. 

If this was a classical Cass., then the primary is way under corrected, 
and the secondary should be hyperbolic.

If it’s not a classical Cassagrain, then. . . . . . .

OK, well today I finally got around to grinding and polishing the back 
of the secondary to see what the heck is going on with its curvature..

Its amazing how much straie  and bubbles are in the secondary, it may be 
early Pyrex, like the primary, but, sure looks spherical to me, at least 
over most of the surface.

So, under corrected primary, spherical secondary, sounds like a 
Dall-Kirkham to me!

Texereau’s book footnotes a reference to Dall and Kirkham’s design in a 
1951 Scientific American, which I will have to get, but this scope was 
supposedly made in 1929, there are 
definite references to it being on Mt. Wilson in 1932, and 1935.

Anyway, if anyone out there has any information, or possible references, 
in regards to when Dall and Kirkham first mentioned this type of 
Cassagrain design, I’d appreciate yor comments, as well as any comments 
on the moral issue of whether or not I should rework these almost 70 
year old optics…

TIA
-- 
Bill Marriott
Woodacre, Ca. USA
btk@pacbell.net

http://www.starlightoptical.com
Optical/ATM projects

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