[ATM] lurie-houghton progress

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

My colleague Nagesh and I have been working on an 8
inch Lurie-Houghton, which needs 2 corrector plates.
All surfaces are spherical, and the convex surfaces on
the corrector plates fit exactly into the concave
corrector plate surfaces. The corrector plates just
have to be identical glass to each other; no exotic
glasses are required. 

Today we made pitch laps for the 2 more steeply-curved
(ROC ~ 5 feet)  corrector plate surfaces, and polished
for about half an hour or so; the glass is much, much
softer than Pyrex and polishes much more quickly. When
we looked at the concave surface under the Ronchi test
(100 LPI) we found that the lines were absolutely,
perfectly straight, which made us very pleased indeed.
Then we put the convex one (**carefully**) on top of
the convex one in our monochromatic light box, so that
we could look at the interference fringes. The fringes
were almost perfectly straight as well! Again, we were
very, very pleased.

Especially since when we had done the same thing the
night before for the 2 other surfaces (ROC ~ 20 feet) 
the ROnchi lines were a total mess, and the
interference fringes looked very much like fingerprint
on my right index finger.

I had heard that when you make surfaces that are very
steeply curved, it is much easier to make them
spherical then if you make surfaces that are close to
being flat. Anybody else had this experience?

This has been a very interesting and educational
project so far. I wonder why there are no commercially
available Lurie-Houghtons and very few amateur ones;
it seems to me to be easier to generate 5 spherical
surfaces than 1 sphere and then 2 4-th degree curves? 

We have had our inspiration from A Comprehensive
Manual for Amateur Astronomers by Rutten and van
Venrooij, as well as the examples of Rick Scott in the
and Aki Lotjonen.

See
http://members.cox.net/rmscott/lh_scope/index.html
and 
http://koti.phnet.fi/lottaki/index1.html

(Unfortunately, the only name we can actually
pronounce of all of those is that of Rick Scott. Maybe
we'll learn the other names if and when we ever meet
them face to face.)

We will soon have to start working on the lens cell in
the NCA's South Bend lathe and to begin the process of
trepanning the 2 corrector plates.

Guy

Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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