Re: ATM mirror testing

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

I do my testing with a TV camera and have noticed that coated mirrors have a
real bright return (duh, what else is new!) and the camera goes through a
period of AGC action as the blade crosses over and it's only when the AGC
stops acting that the true figure comes out.  It's often very interesting as
the decrease in light can exceed the speed at which the camera works and I
can get a dark mirror that will brighten again with the true figure.  I
don't know if this is what you are talking about but if it is, that's what's
happening.  If you are working with your eyes, then the above, of course,
doesn't count.
If you aren't fully polished out, then the light from the pits will reflect
all over the place and you won't be getting the image of the figure but
rather a whole bunch of noise.
The shadows should happen only once and any second appearance of shadows
should be investigated to find out what is happening.  The test, being a
geometric test, allows only one set of darkenings to happen if it's done
correctly.  You might also want to look at the light source and insure that
you don't have a dark spot near the knife edge that is making for the two
episodes of darkening.  Putting the tester about 1" or so in from the proper
location will allow for you to look at the returned light image and it
should be a nice even bright return across the whole image of the LED.
Bob May
My new web space address is http://webu.wigloo.com/bobmay/ or
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and my new email address is bobmay@nethere.com
Bob May