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[ATM] Foucault test : DP=-H2/R or DP=-H2/R+H4/2R3 ??
I've read in the French version of Texereau book "La construction du
télescope d'amateur" that 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.
For most mirors, it doesn't make a big difference and it is lower than the
precision of the deplacement of the knife.
But in my case, I have a very low F/D miror (F/D=3.3) and the second term
H4/2R3 is no more neglictable if it exists really.
Does anyone knows if this term really exist or not for a perfect parabola?
Thanks in advance
Raphaël Guinamard
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