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Re: Negative Focal Length

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Posted by stevec/">stevec on February 23, 2000 07:34:09 UTC

: How can the focal length of a negative lens be found without buying an expensive curvature measuring instrument?

You can make a simple spherometer with a dial indicator,some ball bearings and aluminum plate for less than $25 i have made cassegrain secondarys and determined the negative fl by finding the fl of the concave tool used to grind the convex secondary, a good book which describes how to make several different spherometers is advanced telescope making techniques,volume 2. good luck.

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