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RE: [ATM] RE:anealing
The blank in question (Frankenblank) was for an optical flat. I still have
the monster laying around somewhere. The variations in figure were
noticeable when interference testing against a 1/20 wave reference flat.
Perhaps you would not notice the changes using Ronchi or Foucault, that is,
if the blank had been for a mirror. My experience is that plate glass is not
suitable for optical flats because of the long stabilization time after each
figuring session. With pyrex I can let the flat rest for 1 hour before
retesting. With plate glass I must wait for at least 12 hours. Plate glass
is also softer and thus more likely to scratch.
I buy from Newport because they are cheaper and have a greater selection.
All in all their pyrex blanks have been OK for me (except for Frankenblank,
and I don't really know the reason why this one failed). I buy other stuff
from WB but their pyrex blanks are about twice the price of the ones from
Newport (last time I checked).
Every ATM should try making a set of 10 or 12" optical flats (to 1/20 wave)
using the ABC method. It is a humbling experience. What for? well, punch a
hole in one of them and you can use it for autocolimation testing, use the
other ones to make diagonals for your Newtonians, and so on. Foucault once
said that a flat mirror is like an artificial sky.
Regards,
Julio
-----Original Message-----
From: Mutalib Abdallah [mailto:omegatroid@hotmail.com]
Sent: Monday, May 23, 2005 11:42 AM
To: jsanchez@skipanon.com
Subject: RE: [ATM] RE:anealing
It is easy to check the annealing by inspecting the glass between crossed
polaroids. Newport HAS shipped un-annealed glass. Why would you every
buy from them? And why do you think pyrex is needed? Plate glass works
fine. And why such a thick blank? It will take four hours to cool to
operating temperature at night.
For more information on how to make your own blank, go to
www.megspace.com/science/sfe. You don't need Newport; nobody does.
Willmann Bell is OK.
>From: "Julio Sanchez" <jsanchez@skipanon.com>
>To: <atm@atmlist.net>
>Subject: [ATM] RE:anealing
>Date: Sat, 21 May 2005 15:26:42 -0500
>
>I once bought a 10" by 2" Pyrex blank from one of the well-known (and badly
>reputed) suppliers and ended up calling it the Frankenblank. It seemed to
>have a life of its own and the figure would change overnight, after a week,
>after a month, etc. It seemed like the thing had moods. I suppose it was
>badly annealed, maybe not at all. Since then I stay away from the thicker
>stuff.
>
>As far as I know the only sources for Pyrex blanks for ATMs are Newport
>Glass and Wilhelm-Bell. The latter more expensive than the former but a
>little more reliable. Both claim that they anneal the glass but there is
>plenty of evidence to the contrary.
>
>If anyone can find a reliable, inexpensive, supplier of annealed Pyrex
>blanks from 6 to 24" diameter the ATM world will beat a path to its door.
>All seven of us.
>
>Regards,
>
>Julio
>
>
>
>-----Original Message-----
>From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf Of
>atm-request@atmlist.net
>Sent: Saturday, May 21, 2005 2:07 PM
>To: atm@atmlist.net
>Subject: ATM Digest, Vol 17, Issue 22
>
>------------------------------
>
>Message: 16
>Date: Sat, 21 May 2005 14:57:43 -0400
>From: "john sherman" <atm@mail.johnspics.com>
>Subject: [ATM] annealing
>To: <atm@atmlist.net>
>Message-ID: <200505211457.AA3063349464@mail.johnspics.com>
>Content-Type: text/plain; charset=us-ascii
>
>
>Dave,
>
> >United Lens, a large annealer of all kinds of optical blanks,
>
>My friend just bought 5 large precision-annealed blanks from them. Three
>have to be returned because of poor annealing. I have seen the photos of
>them thru full-size polarizing sheets. Even the "good" one shows Richard
>Schwartz' Satanic Cross. Is there somebody better to buy Pyrex from?
>(Please
>don't say the "N" word!!!)
>
>John
>
>
>
>
>
>
>
>
>
>------------------------------
>
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>End of ATM Digest, Vol 17, Issue 22
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