Re: ATM Preground Lenses Question

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

Yep, the curve generated shouldn't be exactly what the final is going to be.
It doesn't matter what the grit is, whichever is on top (in the traditional
amateur method of grinding) is going to turn concave and the bottom is going
to become convex.  Even if you take very short strokes, this still happens.
The process just slows down as you go to finer grits as you are removing
less material.
I usually recommend to the grinders to stop coarse grinding a few
thousandths of an inch short and that leaves room for getting the right ROC
when you get to the final polish.
Take what the place gives you and ask for about how much the change should
be for each grit.  Also put together a decent spherometer (or buy one) and
learn to use it properly.
Bob May
http://nav.to/bobmay
bobmay@nethere.com