Thank you for the replies and the encouraging words. I will experiment more with MaxIm DL to see if I can tease out more details as suggested; it is exciting to think that I could.
I double checked the apparent cropping of the image. I believe the image area captured is reflecting that the ATIK 420c is capturing about 2.27 arcsec per pixel in my HyperStar configuration (assuming a resulting focal length of 400mm), or an image area of 1.02 x 0.77 degrees (width x height).
Thank you for the feedback about focus.
I tried, for the first time, to achieve focus manually by minimizing the FHWM of one of the stars (via Nebulosity). In hindsight I see that my impatience to get to a series of longer exposures influenced my settling on an out-of-focus setting. I also think that because of the relatively high humidity and the low elevation of my backyard observing site, that I did not have much hope for a true fine focus (I am in Saint Charles, MO, part of the Saint Louis metro area).
Hopefully I can better balance my excitement about using the telescope with practicing the patience needed to learn how to use the telescope and its accessories effectively.
Clear skies,
Jim