Re: [ATM] checking for sphere

["Bob May" <bobmay@nethere.com>]

My technique has been to use a spherometer to see if the measured ROC is the
same over the whole surface.  I'll tolerate about .002" difference over the
surface.  I'll note that a really cheap spherometer can be made by using 3
screws in a plate (even wood!) to set the radius of the circle (3"-4" is a
nice diameter) with one more in the center to measure the depth.of the sag.
No need for actually measuring as you are looking for relative changes in
ROC rather than an absolute value.
You can also cut out a radius on a piece of plastic or metal that you desire
(carefull with the cutting as the curve is really gentle!) and compare that
to the curve that you have generated in the glass.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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