The Bode’s Galaxy (M81) and the Cigar Galaxy (M82) are located in the Ursa Major constellation, which is right outside my backyard. Taking advantage of clear night on 2/14, I decided to see if I could capture these two galaxies. I got everything set up, ready, and started imaging. Two and a half hours later, I started to process the images and boy was I disappointed. M81 and M82 were severely out of focus. I told myself no big deal and I could just wait for another clear night and image them again. Here is the output from the night of 2/14:
Three days later , on 2/17, I tried it again. Thinking I had a much better focus, I imaged the two galaxies for another 2.5 hours. As I was processing the images from that session, the same thing happened! I was out of focus again. How could this happen two times in a row? Taking a step back and do some research on focusing. Turns out, there was still a great deal to learn. The clouds rolled in after that night so this gave me some time to do some research into how to achieve a better focus.
Turning to youtube, I came across this fantastic tutorial by John Blackwell on understanding a Star’s Full Width Half Maximum (FWHM). Huh? What is FWHM? Turns out this four letter F word (not the one you are thinking about) is very important for determining whether your image in focus or out of focus. In its simplest form, the FWHM is a measure of the size of a star. In the program, MaximDL, you can view the FWHM’s of the stars and plot the data on a graph. The brightness of a star is calculated as a number between 0 and 65,000, the maximum value a CCD camera can record. Here is a simplified version from John’s youtube tutorial:
Let’s take a look at two identical stars from my imaging session:
Is the third time really a charm? Maybe? The third time imaging M81 and M82 turned out great because I took the time to learn how to focus better and also spent extra time making sure the focus was great by looking at the first exposures. I highly recommend John Blackwell’s tutorial as it helped me understand a critical part of focusing my images. Here is the result of my third imaging session of M81 and M82: