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Steve W
super member
Reged: 09/27/04
Posts: 148
Loc: Dundee, OR
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I'm considering using a 22" fused glass mirror from Normand Fullum on my new scope. Normand's prices and lead times are very competitive and the fused glass blank saves weight and should decrease cool down time. The only down side I see at the moment is that these blanks are typically thicker than standard blanks (4" vs 1.5" - 2") which will raise my EP height slightly. Has anyone else had experience with these mirrors?
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Steve
18" f/4.5 Obsession #354 with AN/SC
12.5" f/5 Plettstone ultralight dob
Working on a 22" f/3.3 dob
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3539
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there used to be many Hextec and Stablelite fused mirrors around that were made of pyrex.
now you have the hubble and jean guy (normands supplier) made of plate glass.
fast cooldown it a big plus, just dont thermally shock the mirror by washing it with cold water after it has been in a hot trailer or something. plate glass does not like going from hot to cold like pyrex
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Jean-Guy is also doing fused borosilicate, assuming that Normand's web site was talking about a real item a while back. He posts on the ATM List occasionally. The only fused plate mirror I've seen from him was an early one I refigured some years ago - there was a lot of residual stress, to the point some of the posts had cracked off the plates, and horrible print-through as a result. From what I've heard they've improved a great deal, though.
Best,
Mark
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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1234
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Residual stresses....that should have been a REFUSED glass...
Jess Tauber
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Well, I improved it from about 1/3 wave to a nominal 1/10th PVW but it was inconsistent depending on the temp - classic stress example. And hard to measure, what with the figure variation due to print through - I just said it was approx diffraction limited when done, and it really did work a lot better.
Best,
Mark
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