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Old 11-04-2022, 04:43 PM
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mura_gadi (Steve)
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Ok, Black glass blanks anyone? (or easier, better and cheaper glass blanks)

Hello,

Saw this and couldn't resist the thought of some funky black telescope glass.

The prices for the pre-curved blanks are surprisingly good though and the BVC is better* than Pyrex over 400mm for acclimation.

The blanks have between 3-5 F/l up to 20", after that its mostly only two options for the focal length up to 30".

They are thin light weight mirror blanks!

It is not a secured site however... so proceed at your own risk which is a little sad for this day and age.

http://www.bvctek.ca/thin-pre-curved-mirror-blanks.html


*"We have been passed test figures from the Canadian company showing a range of 2.56 -2.64PPM/Deg C, which supports their claims. Note even the worst of the figures quoted, - 2.8PPM/Deg C, - is still lower than Pyrex." from Astrofox Astronomical Instruments website.


**Easier better cheaper = Easier this is soft glass, a lot softer than soda lime and the black colour apparently helps with pit detection. Better = cools down even faster than Pyrex and sandwich is very light you can get to 24" before you break 10 kilo. Cheaper well certainly compared to some pre-curved large blanks I've looked at....

And a page about working with the glass with all the makers spin, but looks like you will need to smooth the backs.
http://www.bvctek.ca/bvc-glass.html
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Last edited by mura_gadi; 11-04-2022 at 06:31 PM.
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Old 12-04-2022, 08:12 AM
Rod
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I have one of his 10 inch meniscus blanks I have started on. Many years ago I ground and part polished a 14 inch F4 monolithic BVC blank. It was 1.5 inches thick.

BVC grinds and polishes very fast. Scratches and pits are easier to see. A fellow club member has made 2 large mirrors from it very successfully.

It’s obviously opaque so you can’t test it for strain. I don’t think that’s been an issue though.

I don’t have any experience of the sandwich mirrors. From what I’ve read there are a few more things to consider - to avoid print through for example.

Rod
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Old 12-04-2022, 11:09 AM
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mura_gadi (Steve)
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Ah, I loved to get to the ASV for the atm workshops, I could save on posting old news for starters...

Great news to hear that people are getting good results from the blanks as well, so tyvm for that.
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Old 12-04-2022, 07:42 PM
Rod
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Hi Steve

BVC only recently became available again and they are probably the cheapest blanks available. It’s good you thought to alert people to them.

Rod
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