Re: ATM 10" help - TDE?

["Dave McCarter" <dmccarter@sympatico.ca>]

> Some photos were out, some inside the ROC, some right at the ROC.

While it must be tempting to take a photo at every millimetre either side of
the ROC when you have an electronic camera, and "film" is cheap, one only
needs two or maybe three images to evaluate the mirror surface in a
subjective way prior to final figuring.

1. With knife edge outside of the RofC at the one third zone. You will see
most of the surface with this.

2. And one outside at the 4/5 or so of RofC, when you can get a really good
idea of how the edge is doing.

And a third one is useful if you have a Ronchi grid, which will negate the
need for the other two, outside RofC with four to seven bands showing. The
curvature of the bands tell you everything you need to know about the
developing surface, even when figuring, until you need numbers.

Dave