|
Yi-Zen,
I guess my first question would be "How was your Ploar alignment?" I have taken
pictures when the ST-4 was guiding between 1's and 3's and still the stars
trailed. I went back to my notes and found that I short-cut the drift
alignment.
Don Spencer
----- Original Message -----
Sent: Thursday, June 12, 2003 8:54
PM
Subject: [APML] Trailed Stars, Large
Errors: Help for a Newbie
Hello
everyone,
I'm a newbie to deepsky astrophotography, and would like to
get some help. During the last new moon period I got together the following
setup:
1) Losmandy GM-8 mount with Gemini GOTO system (rented) with
dual scope platform
2) On one side of the dual scope platform I mounted a
dovetail bar with an STV + camera lens (180mm or 105mm) on one end and a ball
head with a Nikon F4 on the other end.
3) The other side of the dual scope
platform carried a Borg 100 ED.
The STV head was mounted on the
dovetail plate directly with a single screw tightened as tight as possible -
same for the ball head on the dovetail plate.
First problem: I tried to
autoguide with the STV and saw very large errors, on the order of 2-4 arc
seconds, sometimes even larger. Is this normal? I did notice that seeing
wasn't too good, which surprised me somewhat, as I was observing from an
elevation of 4-5K feet or higher (SE AZ). What are the possible causes of
large errors? I'd like to try to investigate this more carefully but would
appreciate inputs on what to look out for.
Second problem: almost all
my shots (except one) came back with trailed stars. The longer exposures seem
to have the longer trails. (I shot mostly with 55mm and 180mm lenses, and also
through the Borg at 640mm.) Most of them were trailed in the NE-SW direction.
Only one was trailed in the E-W direction. The latter shot was of the Rho Ophi
region and the rest were of Cygnus, Mel 111, M101 and Lagoon regions. I am
wondering if this trailing is related to the first problem. What are the other
possible reasons for this? Flexure? Bad guiding? Severe backlash? I thought
that perhaps the ball head was flexing, but there is trailing for the shots
through the Borg as well. I noticed that the camera lens can be pulled away
from the CLA-5 adaptor a little (i.e. the lens does not sit on the flange
tightly) - could this be a source of flexure?
Thanks for any
inputs!
Yi-Zen
_______________________________________________
Astro-Photo mailing
list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo
|