Re: ATM Re: Collimating Newtonians with Laser

[UC007@aol.com]

In reality in laser collimation there are three reflections. From focuser to
primary requires one reflection from secondary. The second reflection is from
primary back to secondary, and finally the third is secondary back to focuser
(we hope). The amount of light reduction is the multiplied value of
refectivity of each mirror at the wave length of light concernec. If each
mirror surface is 90 percent reflective, at the red wave lenth of the laser
then total loss equals 100 percent less 72.9 percent. Total loss is 27.1
percent.  Most mirrors are below advertised reflectivity, due to poor
polishing. Of course star light is only reflected twice to the focus.

Regards,

Bill Fries, EAS