I spent some time last Saturday evening taking images of some galaxies. I wanted to get a good wide field image of M33 in Triangulum which was nearly overhead. M33 (along with the Andromeda Galaxy) is part of our local group. It is fairly large (being relatively close by at 3 million light years) and very faint with a small star like core and some bright star forming regions.
The Starlight Express H9C camera on the 80mm APO refractor at 480mm focal length gave a field of view of almost 1 degree. M33 fit nicely in the frame. I used a Meade DSI camera on the 12″ Meade LX200 at 3000mm focal length as the guide scope. I took about an hour’s worth of 5-minute sub-exposures. Guiding at 3000mm focal length held the imaging camera rock steady for the duration of the exposures. This is the result after stacking and some image processing. I will post a full-size version to the gallery on our web page (http://www.pewaukeeastro.com/messier_gallery.html).
So far, so good. . .
Next, I thought I’d try NGC 7331 in Pegasus. Our web page has an image taken last last fall but it was not guided and very grainy. I wanted to get a nice guided image to replace the old one. This galaxy is MUCH further away (about 45 or so million light years) and is very small in the wide-field view. Therefore, I decided to switch the cameras and change who’s guiding who. I put the imaging camera onto the 12″ telescope with a focal reducer giving a focal length of about 1900mm. The field of view was about 16 arc-minutes. After re-focusing both cameras and re-calibrating the guide software (Maxim DL) I was back in business taking 5-minute sub exposures.
This time, the stars we somewhat elongated in the 5-minute exposures even though the on the guidescope looked like it was tracking well. However, the focal length of the guidescope was so short compared the the focal length of the imager (480mm vs 1900mm) that very small errors in guiding had a large effect on the imaging scope. Even so, the sub-exposures weren’t too bad and I was happy with the results.
then it happened. . .
Instead of seeing something like this:
I got this:
I can’t say whether I was daydreaming or distracted by checking the latest scores or what (I definitely was NOT snoozing!) but the guider lost track of the star it was using for a reference and chose a different one. It then moved the new star to the position of the original star. I was able to re-center the galaxy and carry-on. Sometimes funny things happen when guiding!
Here is the processed image — the full-sized version will appear on our web page: (http://www.pewaukeeastro.com/ngc_gallery.html).
By then I was ready to call it a night.
– Tim
