Re: [ATM] Improving my focault tester / testing skills

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

Matching to ajacent holes is easy, it is when the holes are
further apart (guess where the holes for the outer zones are!)
then it becomes progressively harder to do.
The typical Couder Mask with all of the zones on it makes things
worse as you are also seeing the results of all of the other
zones.  Better to make a mask of just that one zone and then you
can compare the two apertures against each other without all of
the distracctions of the other zones.  Even better is to put a
little bit of light on he mask so that it can be compared against
each side as an additional reference as Smith points out, that
being that ajaccent surfaces can be matched quite well against
each other.
FWIW, there was a  sky darkness meter article in the Sky and
Telescope mag. some years ago that used this principle  to
determine what the darkness level of the sky was at any
particular time.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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