Re: ATM BK 7 ideas

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

The first mirror is a front surface mirror so any material can be used.
Some like the fused quartz for it's good suface finish properties.  The
mirror is near the focus so you are interested in good finish and an
accurate surface.
The second mirror is a Mangin style mirror (second surface mirror with
curved front and rear surfaces) and is usually made of another piece of
glass from the same melt as it's job is to remove the color errors, which
are quite huge from the single lens of the objective, and the best glass to
use is one which has exactly the same indices as the objective.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net