[ATM] Focal Ratio for a Fast 24"

[Mel Bartels]

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At what point would you consider working parabolization into the mirror
during fine grinding instead of waiting for polishing?   Do you have any
ways for a crude test of a mirror figure before it is polished out?  There
had been talk of infrared, but perhaps there are other ways...
<<<



Why would you want to work parabolization into fine grinding? Because it
naively reduces amount of glass to remove during parabolization? But
pre-parabolizing adds time and is unnecessary. Further, time to figure is
best reduced by small certain steps, even if they add up to more overall
glass removed than the theoretical minimum. It seems to me that
pre-parabolizing is a major gamble for an amateur mirror maker, not in
keeping with lowering risk and getting done expeditiously. 

Mel Bartels