Re: ATM Hole in mirror

[andydtg@phoenix.net]

David Reynolds wrote:

>        I have seen several references recently to putting a hole in the
>center of large Newtonian reflector mirrors. What is the benefit of this and
>what size hole are we talking about?

Benefits:

- Easy to do autocollimation test thru hole, about 2" dia req'd

- Use the hole for radial support instead of edge, I've
  done this with mirrors up to 32" dia.

- Use for Cassegrain focus later.. 3-4" dia needed

Disadvantages:

- Can't use laser collimators

- not easy to do yourself with large mirrors

Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net