[APML] needed- an excellent sense of direction

["Bobby Middleton" <bobm@koyote.com>]

Here's one for the guys with a real good sense of direction. I've got an
out-of-square focuser on my newt. I know that's the deal because every time
when I get the laser collimator perfectly aligned I'll get long stars on two
corners of my negatives. These two corners are consistant about having the
problem, although at times it's worse than others. That means one of these
corners is too high while the other is too low, right? The normal method of
squareing in a focuser is getting a hole exactly opposite of the focuser and
aligning the focuser with a laser right on the hole. I have a hole and I
have it aligned with the laser, but I suspect getting that hole exactly in
the right place is easier said than done. I suspect my alignment hole is off
a bit.

I have not been able to detect my focuser alignment hole's mis-placement by
measurement. It appears to be right but obviously something's off. I want to
figure it out by N-S-E-W analysis of my camera composition. Here are two
images typical of my long stars:
http://www.koyote.com/users/bobm/alnitak.htm
http://www.koyote.com/users/bobm/ngc281.htm
Note the long stars at the lower left and upper right of the images.
If I've got it figured right, these corners are the SE and NW corners. (Both
of these images are composed with the 35mm long axis running E-W). Can we
match this known orientation to my focuser with a description of where my
focuser is mounted on my tube?

Picture my 12.5"newt on the east side of my AP 1200 mount (ready for past
zenith tracking). My focuser and camera are on the west side of the tube.
I'm pointed at NGC 281 (packman nebula) and it's 7:30-9:30 pm which means
for this time of year NGC281 is about 1-2 hours past meridian. If I get
directly behind my tube (from tube bottom looking towards NGC 281) the
focuser will be right about on the 8:00 o'clock position of the tube. Your
mission, should you decide to accept it, is to tell me which two of the 4
corners of my JMI 2" focuser need tweeking. To get an E-W long axis
composition, my camera must lie diagonally with respect to the 4 corners of
my focuser. That incomplete description now leaves two possibilities; the
camera long axis is either horizontal or it's vertical. On my setup an E-W
long axis composition with everything described as above has the camera long
axis composituion with the camera horizontal.

I'm sorry for such a laborous description, but I'm in hopes that someone can
get the directional bearings on where my image lies on the film plane, and I
can get an idea of which two corners on my focuser are off. I've had this
mis-alignment ever since I got the newt.
Bobby Middleton


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