[AZ-Observing] A Tale of Two Images...

  • From: "David M. Douglass" <dmdouglass@xxxxxxxxxxxxxxx>
  • To: <az-observing@xxxxxxxxxxxxx>
  • Date: Sun, 18 Jan 2015 11:53:37 -0700

A tale of two images..

Last night, I was working on my Astronomical League (AL) Flat Galaxy (aka
Edge-On Galaxies) observations, and one of my targets was NGC 2820. You can
see the resultant image of that observation here:

The actual target is inside the circle, basically in the center area of the
image.  It was an interesting image, in that the lower right of the image
caught my eye, and held my interest more than the primary target.  In the
lower right is NGC 2805. That was NOT the target, but was captured as a "in
the field of view" item. 

I checked my index of images, and sure enough, I had one for NGC 2805. I had
made that observation on April 29, 2013, for the Herschel-2 program. I went
and took a look. You can see it here:

Yup, that was it. But WOW !! What a difference. Therein begins the tale of
two images.
In April 2013, I was using an LX-200 8" (Alt/AZ). Same camera, but the older
image was set to inner-half (think "close up"). I no longer use that
setting. I really enjoy looking at the wider view, and the surrounding skies
for each object. You miss a lot with close ups (IMHO).

Today, I am using a Celestron 8" Edge, mounted on a CGEM (EQ). The
difference between Alt/AZ and EQ is a major part of the difference in the
images. I was limited to 2-3 minute exposures with the Alt/AZ, and the
longer exposures always generated some star drift. With the CGEM (EQ), I can
go out to 20 min plus with no problems.  My standard for imaging DSO is 5
minute exposures, and a stack of 7 images.

And changes in processing tools, and skills. CCDStack-2 is a marvelous tool.
Thanks to Adam Block for his lectures on how to use that tool.  Late last
year, I learned about using dithering with the stack, and now I always do a
"Data Reject" clip min/max."   Another major change (improvement).  PS CS3
is still a valuable "finishing up" tool as well. 

Amazingly, I have a better image of NGC-2805 today, captured "by chance" as
background, than when it was the primary target in 2013. As the saying
goes..   Ahhhhhhh, what a difference a day (or year or two) makes.

It was an interesting observation to me (the two images, and the
differences, and why)..
Thought I would share the experience.

David M. Douglass
dmdouglass@xxxxxxxxxxxxxxx (secondary)
david@xxxxxxxxxxxxxxx (main)
Cell (602) 908-9092

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