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Old 06-01-2019, 04:39 PM
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Is there any demand for this round window?

A friend of mine has this round window which would make a good telescope lens, however it's corrugated. Is there any demand for it, and if so what price might it fetch? Dimensions coming soon...
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Old 06-01-2019, 04:48 PM
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RickS (Rick)
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What makes you think it would make a good telescope lens?
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Old 06-01-2019, 05:06 PM
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Oops I think I meant to write mirror (for a Dobsonian) instead of lens
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Old 06-01-2019, 07:11 PM
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For use as a primary mirror the glass would have to be reasonably thick.

The Diameter / Thickness ratio should not exceed 10:1 to be safe, e.g. a 250mm diam glass should be no thinner than 25mm. However I have read some amateurs going to a 20:1 ratio with no problems.

Also you can't use tempered or toughened glass as it will shatter during the grinding process.
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Old 07-01-2019, 09:45 PM
Wavytone (Nick)

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That's just an old-fashioned piece of window glass with ripples, popular in the 1950s in front doors. Useless for telescopes.
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Old 08-01-2019, 10:06 PM
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Thought I'd provide an update based on the information I received from multiple sources, in case someone else has a similar question as I did. The corrugation is not a big problem but obviously it's not ideal as it would require extra work to smooth (can also be used for slumping). The main thing is that the glass is thick enough which Bill already explained above (thank you), and that it's not tempered which could make it explode during grinding. Unfortunately this glass doesn't meet those criteria which makes it unsuitable.
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