Re: [ATM] Masking a TDE

[Bill Prewitt <bprewitt@neo.rr.com>]

> I've just completed polishing a 6" f7 pyrex blank.  I put it on the foucalt tester and noticed that I have a small 1/8" to 1/16" wide turned edge on it.  I've just put everything away for the day but I kick myself for not measuring the depth of the edge.
> Anyway, I'm thinking of just "living with it" so I can parabaolize this mirror and the move on to other ATM projects and here is my question:
> I've heard alot about masking the TDE (see Berry and Kreige regarding large thin mirrors) but I've never seen any info on how this is done.  Do I paint the aluminzed mirror.  Do I build the mask into the mirror cell via some sort of vignetting device.
> Can any one point me to info regaring some easy/elegant/effective masking techniques.


Since I got a Ross null lens, I've discovered that several of my mirrors 
have more TDE than I knew about.

Here are two methods:
For a small mirror, center it on a turntable and use a Sharpie to 
blacken the edge.
    (Quick & easy but bad if you ever plan to clean it with a solvent)

Buy a sheet of thin poster plastic at a craft or office supply store
Mark outer and inner edges of the ring, then cut out with scissors.
Spray with Krylon Ultra Flat Black.
Fix to the edge of the mirror with several pieces of tape.
With this method, you can remove the ring before cleaning the surface.

           Bill Prewitt
       www.astrocaver.com
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