Starlog October18th, 2024, 7:30 p.m. local time
Each night photographing Comet A3 has presented its own challenges. On this evening, the problem was focus. On the prior two evenings I was able to easily leverage the Moon to get decent focus. However, on this night the Moon was still well-hidden in my East sky.
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I tried using the still visible Arcturus, but it was too faint through my neighborhood pollution. I then attempted to point the camera nearly straight up at the Summer Triangle asterism, specifically its brightest star Vega, but this proved too awkward.
What saved the night were all the airplanes going in, out, and around O’Hare International Airport. The planes are not exactly infinity focus, but they are sufficiently distant to get the needed focus into the right ballpark. This article’s accompanying picture was taken after focusing the lens on a plane.
At this time of the year in the Northern Hemisphere, the West sky after Sunset is pretty boring, especially in light-polluted areas. The main constellations around Comet A3 – Corona Borealis, Ophiuchus, and Serpens – are not household names. The surrounding stars are not relatively very bright, with only the aforementioned Arcturus and Vega being the closest stars of note.
Thankfully the camera can capture far more light than the human eye, so there are many stars in this image. Below, I outlined the three constellations mentioned above, and highlighted the star Unukalhai, which I have been using as my anchor guide star as A3 rises higher in the sky each night.
Equipment Used:
- Canon EOS Rebel SL3
- Sigma wide field lens, 17mm focal length
- f/2.8
- 0.8 sec exposure
- ISO 6400
- Touchups in PaintShop Pro and AfterShot Pro
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Focusing a DSLR on the stars can be a bit tricky. The auto-focus on these cameras will not focus on them because they were not designed for astronomy. Even the manual focus is a problem, with no fine tuning.
To a degree my focusing on Arcturus relied heavily on muscle memory for the general location where I usually set the lens focuser.