Re: Restoring-Meade 6 inch

Steve Strickland (lensnut@tpoint.net)
Fri, 7 Jul 1995 13:52:03 -0500

>To All,
>HELP, I've been lurking for a few months trying to decide what to start
>pushin glass on first. I made a trade for an old 6 inch f5 newt tube
>assembly minus the diagonal and holder. After a not too close inspection I
>found that the primary would need a recoating and the tube will need a
>little 'glass repair, not bad yet. I thought well, now might be a good time
>to build that foucault tester and check out the primary before I send it
>out for a recoat. My question is what time is recommended? I have a copy of
>Neale E. Howard's "Standard Handbook ForTelescope Making" and a paper back
>version of Texereau's "How to Make a Telescope". one talks a bout slit type
>and pinpoint lights. Also, anyone know what size diagonal was standard on
>ths scope, my guess was 1.83 or 2.1 or there abouts. If there is a FAQ
>covering this I would appreciate it if someone would E-Mail a copy. Thanks
>and if some one lives in the far North Dallas area(60 miles) that would be
>willinf to demonstrate the foucault test that would be most appreciated.
>
>jim.mcglynn@smalltownbbs.com
>---
> * WR 1.31 # 624 * Turn out the light and turn on to Astronomy

There's no such thing as a standard sized diagonal. For an in-depth discussion and equations see Kenneth Novak's "Newtonian Notes".

Concerning the Foucault tester, I can't recommend either slit or pinhole design. The "slitless" version is clearly superior and much easier to construct. A number of slitless designs have been published in the standard literature.

Also, watch out for Neal Howard's Foucault reduction math, he uses a flawed assumption that yields false results. Texareau's reduction methods are flawless, but ponderous. Try the Milles-Lecroix method. It's as accurate as Texareau and about as simple as they come. The method was described in detail in Sky & Telescope a few years back. It's also been described in Amateur Telescope Making magazine.

There are several good telescope makers in the Texas Astronomical Society there in Dallas and a large number in the Austin Astronomical Society where I'm located. The TAS has a library containing all relevent information.

Steve 

--
Steve Strickland
Lensnut@tpoint.net