Re: ATM laser test for pitts

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

You are going to be getting a reflection because the bare glass has an
approximate 4% reflection!
What you are looking for isn't the reflection but rather the scatter (which
also occurs on a purely good surface) of the light by pits that are on the
surface.  Go compare a piece of window glass or other fully polished out
piece of glass for what you are looking for and compare it to what the
appearance of the mirror's surface was before you finished the polishing.
I'll note that the laser test is really a hard to determine one if you
aren't familiar with it.  I prefer to do other tests like an edge
illumination test (put the light in at the edge of the mirror and pits show
up as bright spots as well as dirt, etc. as the light bounces off of the
surface internally on a polished surface as it is at more than the Brewster
angle), looking at the surface with a reflection of the sun near the target
area with a 10x loupe, just inspection of the surface with a loupe, placing
on the Foucault tester and seeing if the light from a nearby very bright
source produces any light parts on the mirror's surface (diffraction of the
edges of the pits will make the areas that aren't polished properly glow
from the off-axis light, brighter as the angle decreases until the light
reflects back to the eye from the polished surface) and other tests.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net