Winter 1999

A New View from the 36-inch Telescope
by Dr. Bruce Weaver

A byproduct of this summer’s installation of the DFM control system was an uncollimated
36-inch telescope. The upper left image shows the famous Ring Nebula and at the right a blowup
of one of the star images before collimation (alignment of the optics in the telescope). Conceptually,
this is an easy job: the two mirrors of the telescope system should each be centered about an optical
axis, should be pointed in anti-parallel directions, and should be relatively closely aligned with
the mechanical axis of the telescope. This image shows a well-known optical aberration called
coma, characteristic of a misaligned Cassegrain optical system.

This image of the Ring Nebula, above left, and part of the open cluster M 38 shown at right,
show the results of two attempts at collimation. The smaller images no longer show the extreme
coma and are less than half the size of the first images. They each are less than two arc seconds in
diameter – probably a combination of remaining aberrations and atmospheric effects. This would
be good enough for most telescopes at most locations, but we intend to try to improve it
some more when the excellent seeing conditions of summer return.