A Lesson in Field of View and Apparent Size of Deep Sky Objects

It was another crystal clear night on February 10th so I decided to do some deep sky imaging.  I really did not know what to shoot that night so I turned to the hand controller on my Celestron CG-5 GOTO mount and I started slewing to various objects in hopes I could find an unobstructed patch of sky.  After spending 30 minutes trying to find something to image, I slewed my telescope to  NGC 3395 and 3396, a pair of interacting galaxies in the constellation Leo minor.  After focusing the image, I programmed the number of exposures in in the Luminance, Red, Green, and Blue (LRGB) filters and I 2 hours and 26 minutes later, I began processing 34 sub exposures.  In my mind, I was thinking that the pair of galaxies I was shooting would fill quite a bit of the frame I was shooting.  To my surprise, after successfully processing the image, I noticed that the pair of galaxies was quite small.  After getting over the initial shock, I started to look closer at the image.  Not only did I capture NGC 3395 and 3396 but also NGC 3340, 3424, and 3413 showed up in the image as well.

NGC 3395 3396 3340 3424 3414

NGC 3395 3396 3340 3424 3413

After discovering how small the galaxies were given my apparent field of view (FOV), I decided to calculate my FOV for the telescope and the CCD camera.  After plugging in my telescope focal length and and my CCD sensor size, I calculated my full field of view of my images are 74.8 x 99.7 arcmin (an arcmin is a unit of measurement in astronomy).  After doing some research, I discovered that NGC 3395 is 2.1 x 1.2 arcmin and NGC 3396 is 3.0 x 1.2 armin.  Needless to say, the apparent size of the those galaxies is pretty small given that they are 85 million light years from Earth.  If you want to see the original uncropped image, you view it here:

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