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Re: [ATM] Foucault test : DP=-H2/R or DP=-H2/R+H4/2R3 ??
Thanks for your reply Jim and Vladimir.
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.
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?
Thanks a lot for your reply because when I calculated the H4/2R3 , I found
it was 0.056 mm at the edge of the mirror and since the mesurements have a
precision of 0.01 mm, I thought my wonderfull mirror was maybe bad... I was
VERY disapointed...
Raphaël Guinamard
----- Original Message -----
From: Jim Burrows <burrjaw@earthlink.net>
To: <atm@atmlist.net>
Sent: Saturday, May 29, 2004 6:37 AM
Subject: Re: [ATM] Foucault test : DP=-H2/R or DP=-H2/R+H4/2R3 ??
At 2004-05-28 23:13 +0200, Raphaël Guinamard wrote:
>the general formula (for any type of curve) of the
>longetudinal aberation DeltaP is given as DP=-H2/R+H4/2R3, where H is the
>radius of the zone and R the curvature radius of the miror.
>For the parabola, the formula is given as DP= -H2/R, but without saying if
>the H4/2R3 is neglicted or if simply doesnt exist.
After nearly exhausting my supply of scrap paper, I agree (down to a sign)
that DP (position of the KE) = H²(1/R + H²/2R²) is exact for fixed-source
at the paraxial CoC and a parabola. As I said before, H²/2R is exact for
moving-source and a parabola, so the (small) fourth-order term is the error
in the usual assumption that fixed-source readings are twice moving-source.
Note that the formula doesn't work for "any type of curve" - only a
parabola.
-- Jim Burrows
-- mailto://burrjaw@earthlink.net
-- http://home.earthlink.net/~burrjaw
-- Seattle N47.4723 W122.3662 (WGS84)
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