ETX TECHNICAL TIPS Last updated: 26 January 2006

Subject:	ETX125PE Smartfinder parallax solution
Sent:	Wednesday, January 25, 2006 20:10:56
From:	Deborah Pickett (debbiep-etx@futzle.com)
I thought I'd share this little trick I applied to my Mum's ETX125PE
Smartfinder to help her do alignment.  She's a newbie to anything bigger
than binoculars and was hoping that the PE's auto alignment feature
would be hassle-free.  But the scope still has to be aligned to two
stars, and that was proving difficult because of the Smartfinder.

I'd never used red dot finders before seeing the one on Mum's PE, and I
wasn't very impressed with this one.  The amount of parallax that you
get between the dot and the firmament is pretty serious: moving your
head can move red-dot/star alignment by a couple of degrees, which was
enough to stop Mum from having any chance of finding the alignment star
in the telescope eyepiece.  I was pretty sure that the Smartfinder lens
was correctly mounted, because it did go into the holder with that
satisfying click.

So to eliminate parallax and make sure that the eye is always in the
same line behind the Smartfinder lens, I picked a point somewhere
central on the Smartfinder lens, and drew a big crosshairs on it in
black permanent pen.  Now the routine to centre on an alignment star is:
  (a) align red dot with crosshairs by moving head;
  (b) align red dot + crosshairs with star by using AutoStar;
  (c) switch to eyepiece and spiral search for alignment star.
I found that when all three (red dot, crosshairs, star) are aligned in
the Smartfinder, the alignment star is in the supplied 26mm eyepiece's
field of view, or at least close enough for spiral search to work.

By doing this I was able to cut two-star alignment down to about a
60-second operation, and Mum was able to do it unassisted one night this
week.

This little tip might help some of the other less-experienced users of
the PE and other so-called "automatic alignment" scopes to get to actual
object viewing more quickly.

Deborah Pickett
Melbourne, Victoria, Australia

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