From: David Margrave 
To: atm{at}shore.net
Reply-To: David Margrave 



Hello,

I'm going to be particpating in the 8" refractor class at the western
washington university telescope optics workshop.  I want to prepare a few
things in advance: spherometer and wedge tester.

For the spherometer, there seems to be a lot of talk back and forth about
what is suitable for a dial indicator/micrometer.  Some people have said
that the cheap .001" dial indicator is fine.  Others say that you need
.0001", which would require either a micrometer spindle, dial test
indicator, or precision dial indicator.  I have found .0001" dial
indicators with very limited travel, .0005" with suitable travel, and
of course the standard cheap .001", but nothing of the sort that Roger
Ceragioli calls for in his instructions: .0001" with 1/4" travel.
 Is it simpler to just take a hacksaw to a micrometer to salvage the
spindle?

What size base should I be making for working on an 8" lens?  I'd
guess 5-6".  I have access to a machine shop which I'll make use of
for this project.   Should I try to make a fancy base with multiple tapped
holes
for the feet, or just keep it simple and permanently fasten the feet. I've
seen some plans for adjustable spherometers of this sort which seem
interesting.

For the wedge tester, I think I've got the general idea.  I'm going to take
a sheet of melamine (laminated particle board), and put in some threaded
inserts for holding the feet and the stops, and for the dial indicator
post.    No need for metal or high precision in the construction
of a wedge tester, right?

I have an idea for a relatively simple do-it-yourself optical tube: with a
router cut some rings out of aluminum plate, take a sheet of aluminum and
run it through a slip roll, put a 'step' on one edge to make for a prettier
seam, and then screw or rivet the skin to the frame of rings.  I don't have
the background to make the design decisions however (how many rings, how
thick a skin, etc).  For the lens I'll be working oon, I think I'm looking
at a 10' tube, so I may build it in two or three sections which can be
bolted together.  I'm also seeking information on lens cell design.

Thanks,

Dave

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