From: "Mel Bartels" 
To: "ATM List" 
Reply-To: "Mel Bartels" 


Also matching the detector's spectral response to the eye is important.
I've seen 10% to 50% errors by not taking this into account.  (I presume
the goal of your exercise is to measure coating efficiency for visual use).
Another way to take background into account simultaneously is to image the
background and reflected mirror image onto the same frame.  Or to image one
reflection with many reflections onto the same frame.  Perhaps the latter
might be of some use - if you can get a dozen reflections into the image,
then that might increase accuracy.  You might be able to get a thin strip
of every odd reflection in the image too.  Then you could easily deduce the
reflectivity of the 2nd mirror being used to make the multiple reflections
along with the reflectivity of the mirror in question.

Mel Bartels

--- BBBS/NT v4.00 MP