Re: ATM making maksutovs

[Anthony Stillman <atmer@flash.net>]

Kreig, others,

I am in the process of making a Maksutov. For me the inspiration came with
acquiring a reasonably-dimensioned piece of glass, BK-7 by all indications,
in a horse trade. It took me years to stumble across the chunk. If I were
to buy it new, I would go to a dealer, United, Newport,...but remember,
fortune favors those who make their needs known.   Upon getting the glass,
I was propelled toward making tools to process the blank.  I am still
performing this step, and have had time to push about a design that meets
my requirements, namely f/12, about a half an aperture of bfl, as little
obstruction as possible, and the secondary surface is between 6mm and 12mm
from R2.  I've bounced around a final design in OSLO and am close enough to
know approximately what the CT and radii are of the corrector.   Of course
if someone wants to display a prowess for design and publish their
prescription, I would not be offended. I'm considering designs where the
bfl is as little as 40% of aperture.

At this point I've trepanned the corrector glass. The remaining surface
defects will out with generation. I thought about hand hogging--this lasted
for about 15 min. with 60 grit and an old tool. After that, I started in
earnest re-working my biscuit cutter into a generator. I haven't gotten as
far as I would like with this, but,...

Frank Ward mentions the  "...small booklet published during the 60's by
Millard Fillamore.  Sky Publishing still sells it."  Actually it's Warren
I. Fillmore, and while I agree it's an excellent booklet, there are a few
ommisions and I come away with the feeling that only the most anal
retentive ATM can even dream of making a Maksutov.  I think one of the nice
aspects of having OSLO to play with, is how it helps in understanding
tolerances and hence where to put the retentive effort and where not to
bother.

I'm planning to post a description of my generator when its fully
operational. I'm trying to stick to the do it so it gets done credo and
worry about the shoe strings and sealing wax it's held together with later.

As for exterior telescope design, I was impressed by Gary Logan's 12" Mak
at Riverside this year. He had brought it up before, but either I wasn't
there that year or I just didn't have Mak on my mind. Most notable was
Gary's use of two concentric tubes to hold the optical elements. Air was
circulated between them to thermalize the closed inner tube assembly and of
course the two thin-walled light weight tubes separated by about 30mm
behave like one 30mm thick tube which hardly flexes at all.

As for how I might change what I did, ask me tomorrow.

Anthony