RE: ATM Collimatior Question

["Jim Fly" <jfly@hiwaay.net>]

> From: Matt Devine <mdevine@nuera.com>
> To: atm@shore.net
> Subject: ATM Collimator Question
> Date: Tuesday, July 29, 1997 12:06 PM
> 
> What is the difference between a Cheshire Collimator, and an Auto
Collimator.
> Some information indicates they are both needed.  Thanks...

The "classic" Cheshire eyepiece is a hollow tube with a reflective ringed
surface set at 45 degrees to the focuser optical axis.  There is a small
viewing hole at the back end for looking through the the center of the ring
toward the secondary and another larger hole cut in the side of the tube
directly in across from the 45 degree surface for illumination.

The "autocollimator" is similar except that the reflective mirror is set at
90 degrees to the focuser axis and there is no illumination cutout.

To effectively use either in a Newt, a center spot of appropriate size must
be put on the primary mirror.  The Cheshire is used to adjust the primary
alignment and the autocollimator for secondary adjustment.  Typically, an
alternating, iterative procedure using both is required for correct
collimation.

Jim Fly
CATSEYE(TM) COLLIMATION
jfly@hiwaay.net