Re: ATM Star test with mirror stopped down

["Bill T." <twentiethwave@hotmail.com>]

Stathis Kafalis wrote:
> Has anybody tried, to interpret the star test with increasingly masking
out
> the mirror surface? I mean, you start with full aperture, and then stop
down
> inch by inch, to see how the diffraction patten is changing.

During figuring, with/without mask comparisions are very informative.
Under most circumstances it gives you a reference for what a good edge
SHOULD look like (the masked version) versus what your edge DOES look like
(unmasked).  You even get to see the consequences of the current edge
condition, at least on planets and the Moon.

Comprehensive testing with a series of ever smaller diameter masks might
usefully pull the inner zones out of the "diffraction soup," so that these
zones one by one become easy to evaluate as isolated edge zones.

Bill Tondreau