RE: [ATM] how accurate is the foucault test

["Richard Klappal" <klappal@xnet.com>]

If you are using the Texereau based program to do your data reduction, you
calculate a "suitable constant" in line 9 of the analysis table. This
constant is the correction to be applied to the tape-measure supplied radius
of curvature.  While this works for the calculation, you still don't have a
radius of curvature value that is better than, perhaps, +/- 1 mm.

On the other hand, focal length accuracy to that degree is not necessary.
What you do need is deviation from the focus point, which is what you have
after you subtract out that "suitable constant".

Rich


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
Of David Williams
Sent: Thursday, 20 May, 2004 15:20
To: atm@atmlist.net
Subject: [ATM] how accurate is the foucault test


Hello

I wondered how accurate the foucault test is because once a person knows
that the light or the knife is close to where it should be (inside or
outside of focus) how will you know what the focus is.  Won't you have to
rely on something crude like a tape measure to roughly measure the focal
length?

Can someone talk about the Couder mask.  This sounds like something
interesting.

Thank you for your help.
David Williams
dwilliams1128@earthlink.net
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