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Re: [ATM] Foucault test : DP=-H2/R or DP=-H2/R+H4/2R3 ??
Jim
I send you my control paper off list. Thank you for your offer to have a
look on it!
I don't understand when you say "he wouldn't use either formula because, as
we said, it just
applies to a parabola"
When the optician measure the differences DP (what in french we call the
"tirage") he has to compare them to the perfect parabola, no?
I don't know much of the foucault test, but I though he has to compare his
measurement DP to the theoritical measurement of the perfect parabola which
is DP=-H2/R with moving source or DP=-H2/R+H4/2R3 with fixed source. Am I
wrong?
In fact at first (before you explained the difference in perfect parabola
for fixed or moving source) I thought the only formula was DP=-H2/R+H4/2R3
and he had neglicted the H4/2R3, which would lead to false results
Raphaël Guinamard
----- Original Message -----
From: Jim Burrows <burrjaw@earthlink.net>
To: <>
Sent: Sunday, May 30, 2004 1:34 AM
Subject: Re: [ATM] Foucault test : DP=-H2/R or DP=-H2/R+H4/2R3 ??
At 2004-05-29 08:08 +0200, Raphaël Guinamard wrote:
>Jim: the second term is H4/2R3 or H4/2R2 as you wrote? It make sense to me
>that is should be homogene to m in the dimension equation.
Oops, shoulda used more scrap paper <g>, yes, it's H4/2R3. Writing it
pretty: Foucault KE distance from mirror vertex f = R + 2x + 2x²/R, with x
= parabolic mirror surface height at zone radius H = H²/2R, and fixed
source at R.
>My miror is a 24" f/3.3. On the control paper the optician gave me it is
>written "mobile source".
>So he didn't make error. Am I Right?
Man! A really fast 24" - quite a project! If the optician did it
correctly, he wouldn't use either formula because, as we said, it just
applies to a parabola. One should calculate the surface profile directly
from the readings and then find the RMS deviation from the best-fit
parabola. If the readings (table of zone radii and corresponding KE
positions) are on that control paper, e-mail them to me and I'll give you a
second opinion.
-- Jim Burrows
-- mailto://burrjaw@earthlink.net
-- http://home.earthlink.net/~burrjaw
-- Seattle N47.4723 W122.3662 (WGS84)
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