Re: ATM Robo-Foucault, Image intensity, and Changing knife edge readings

["Bob May" <bobmay@nethere.com>]

Dan, the only thing that I don't see you doing is to insure that the min and
max values of the image of the mirror are not 0 and 255 (assuming a 8 bit
grayscale) but rather some other value inbetween that insures that the image
isn't clipped at either the high or low end of the scale.  Otherwise, you
are going to be getting the right values for the test.  For an experiment,
take the readings on the 25% or other value and you will see that things
will shift.  The proper point to do the measuring is at the 50% point
between an illuminated and not illuminated zone.  Anything else produces
errors due to the way that the Foucault test blocks the light from the
mirror.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net