Author Topic: 10" f5 Pyrex Mirror Blank - "Polished, Not Figured" - Questions  (Read 87 times)

Leon Ware

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10" f5 Pyrex Mirror Blank - "Polished, Not Figured" - Questions
« on: December 28, 2017, 09:41:46 AM »
Got this from a recent buy of astro stuff. Going by what is written on the box it is a "10" f5 Pyrex blank, tapered thickness, concave surface f5, polished, not figured". It is about 1" thick.

However I'm a bit confused about this as while one side is indeed concave, the other side is convex about an equal amount. I've never ground a mirror but as I understand it one way of doing so is to use a similar piece of glass to act as the grinding tool for the actual mirror. Is that the case here? I wouldn't expect the non-working side of the tool to be concave. Perhaps if this was a tool the decision was then made to make the tool into a mirror as well?

The concave side is indeed quite smooth, at least to the naked eye, and looks like it would be ready for coating but I've never seen a 'ground but not figured' mirror surface before. The convex side is rougher. Sagitta is about .117 which works out to about f5.3.

Any comments/suggestions welcomed.

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