Re: [ATM] getting the foucault test right

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

David Williams wrote:
>
> PS What does anyone think about the couder mask that I made, here it is:
>
>
http://www.atmlist.net/contrib/dwilliams1128-at-earthlink-dot-net/20%22Teles
cope%20Stuff/CouderMask20Inch.jpg
>

A few tings come to mind:

In general, I think using a center zone is a bad idea - it behaves
differently from other zones and cannot be read to a matching precision - at
the very least, exclude the part "behind" the secondary. At least "modern"
evaluation programs don't need a center reading, and I think it is better to
skip it than risk being misled by a poor reading.

Assuming the knife edge is vertical, the upper/lower margins of the openings
should be horizontal, not tilted. The light distribution is determined along
any horizontal (=perpedicular to the KE) line, and the parts not so bounded
can be confusing. A central zone like a "tilted strip", as I suspect yours
is, is doubly confusing.

The pieces of tape partially covering the openings are not meant to be there
while testing?

And I would expect the mask to have more zones - or at least you would use a
few masks with different zones - this can be helpful if you can change them
without risking to upset the setup...

You may find these helpful:
http://www.atmsite.org/contrib/Carlin/couder/ and the associated
http://www.atmsite.org/contrib/Holm/coudermask/couderma.html

good luck,

Nils Olof


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