Re: [ATM] The zonal Foucault test is free of inherent correction

["Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>]

Mike,

> b) He uses rather more zones than is common for ATMs. He recommends a mask
> width of f/300, which would produce a 15 zone test in an f/5 mirror
> regardless of mirror diameter.

That would result in 60 openings, or 30 zones.
Each mask opening would be only 1/60th of the mirror diameter, which I
consider pretty small for most f/5 mirrors.
Or is his f/300 actually ROC/300?

> d) Linfoot's basic results were for a point light source. He considered
> sources of finite extent and concluded that they have no significant
effect
> on measurements. So far I've only considered a point source.

The slit he used was "not much wider than 0.001" ", which seems to be very
narrow and will cause noticable fringes. I believe he even mentions those
where he describes the measurement process.

The point of the article was to show that geometric optics approach to
foucault test gives results that do not correspond with reality, and that
wave optics does.
In my opinion this may be the case for the setup he uses (many small mask
openings, very thin slit), but in setups used generally by ATMs the
difference might not be as obvious.

I haven't studied the article thoroughly, so this opinion may well be wrong.

Arjan te Marvelde

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