Re: [ATM] lurie-houghton progress

[Kevin Whitefire <chaosopher23@yahoo.com>]

How thick would the glass need to be for a 13.25"? 
Would this design work on a primary of f/3.12?  

Kevin

--- Guy Brandenburg <gfbrandenburg@yahoo.com> wrote:

> 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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> 


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