Re: [ATM] The zonal Foucault test is free of inherent correction bias- some supporting graphs

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

From: "Michael Peck":

>
<http://www.atmlist.net/contrib/mpeck1-at-ix-dot-netcom-dot-com/ipz1z10.png>
> shows intensity cross sections through zones 1 and 10 at their respective
> nulls. This confirms what I thought was one of the more interesting claims
> of Linfoot. The zone 1 profiles are mirror images, while those for zone 10
> are directly similar. I could see this being a source of "personal
> equation" bias, and it might be interesting to try to confirm it on a real
> mirror.

"Mirror images" they are ;-)

In the "theory" section of
http://web.telia.com/~u41105032/couder/zcalc.htm
I have suggested a reason for the non-mirror-symmetry of the outer zones.
For a constant relative zone width, you will have more and more "tilt" of
the intensity profile the farther out you go - for an isolated inner zonal
opening I believe you would have no tilt at all (you could no doubt check)
but apparently the interaction between the openings tends to raise the
intensity near the inner edges. Probably that is what Linfoot says too,
hidden from a mathematically dense person such as me.

My approach to zonal width is to have an acceptable "tilt" - using
Texereau's standard mask for 8" as a guide.

However, the 3rd order term of the polynomial expression can be significant
near the center, and I think its influence can be seen in Linfoot's figure
8 - the upper curve is a little lifted in the middle, the lower a little
depressed. In order not to have this change the profile too much, I think
for the inner zone, the inner radius should be no less than half the outer
radius.

Nils Olof



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