ATM "collimating" diagonals

["Frank Schiralli, Jr." <schiralli@mindspring.com>]

List:

A few days ago, someone posted a message regarding a wandering laser
collimator beam when racking his JMI focuser in and out.  He uncovered this
apparent anomaly while attempting to collimate his scope.

That poster's experience got me curious.  Further spurred by Thierry
Legault's aricle on high resolution imaging in this months issue of S & T,
I decided to check all aspects of the collimation of three of my scopes,
comprising two newtonians and a SCT.

Naturally, the newts don't use a star diagonal.  I found no errors in
either the 6" or the 16" when racking their respective JMI focusers in/out,
nor when rotating the 2" to 1 1/4" adapter within JMI focusers.  So far so
good.

The following was discovered in the SCT (and here is where I need some sage
advice):

with the star diagonal removed and the JMI Motofocus in place w/ a 2" to 1/
1/4 adapter in place on the visual back, collimation was fine, with the
laser beam returning dead on to it's point of origin as viewed easily
through the corrector plate.  As with the newtonians, rotating the adapter
did not disturb collimation at all.

Inserting the Vernonscope star diagonal (at 12:00 position) collimation was
still fine.  However, rotating the star diagonal 90 degrees clockwise (as I
often do to view comfortably) resulted in a fairly dramatic shift of the
laser beam off the return path.  I repeated this exercise with the standard
Meade star diagonal (JMI motofocus off the setup), and the results were
similar in that the collimation was fine in only one orientation of the
star diagonal.

I examined both diagonals, but disassembled only the Meade. The Meade has a
rectangular plane mirror with rounded off corners and four cork shims that
keep it snug in it's machined aluminum housing, but no ability/mechanism
for adjustment.

How important or degrading to the image are these apparent misalignments??
Do I need to find a way to make minute adjustments of the diagonal using
three small nylon screws or perhaps some shims??  Any comments, ideas,
suggestions??

Thanks,

Frank Schiralli, Jr.
Member, Astronomical Society of Long Island (ASLI)
N 40* 54' 28"
W 73* 19' 22"
E-mail schiralli@mindspring.com
Web Pg. http://members.tripod.com/~AstroImager/index.html

Law Office Web Page: http://www.angelfire.com/ny3/schiralli/