Re: ATM coatings

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

<<He quotes the Ohara catalog showing transmittance values for some common
glasses. In the optical wavelengths the values are above 99%. >>
The transmittance values are for the transmission of the light through the
glass, not including the entrance and exit losses.  Thus you do get values
above 99%.  I'll also note that the reflectance does vary but the 4% value
is the thumb at work here - if you use that value, you get almost exactly on
for glasses in the middle of the glass curve and you're not too far off for
glasses at the ends.  Remember that the reflectance occurs when you change
the refractive index (RI) and is 0 at a 0 change of RI.  Thus, a cemented
lens set with a cement that has approximately the RI midway between the two
lenses will have very little reflection in the middle of the lens set - a
reason why cemented lenses are so desirable for many.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
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