[ARC5] WHINK and crystals - plate glass.

[Richard Knoppow]

----- Original Message ----- 
From: "J. Forster" <jfor at quikus.com>
To: <kgordon2006 at frontier.com>
Cc: "ARC-5 Maillist" <arc5 at mailman.qth.net>
Sent: Friday, June 28, 2013 12:37 PM
Subject: Re: [ARC5] WHINK and crystals - plate glass.


> Your point is well taken.
>
> Some people use a 'figure 8' pattern and rotate the plate 
> frequently. Even
> if the surface of the plate eventually does become a bit 
> dished, the
> curvature is over a much, much larger area than the 
> crystal, so minor
> dishing of the plate still looks locally flat to ther 
> crystal.
>
> It's mostly a matter ow how much is too much.
>
> On a related topic, I was just at a Michaels Craft Shop. 
> They have several
> things for glass etching. There is an etching cream. I( 
> think the stuff
> could be made into a water solution and used for xcrystal 
> etching. The
> brand was something like Armor or Armour. A few ounce 
> bottle was about
> $12. It was an ammonia-flourine compound. If you are 
> interested, Michaels
> has a web site.
>
> -John
>
   I expect you could find a lot of useful information in 
books on amateur telescope making.  I think people still 
grind their own mirrors.  The difference is that one wants 
the surfaces of the crystal to be flat and parallel while 
the mirror is parabolic.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com