Star Haven M31

As usual, between equipment issues and weather issues, I got much less than I expected. But it was a good time with friends from the club and I did get some images.

I’ve shot constellation portraits using a 28mm lens (a “normal” lens on an APS-C sensor), and much longer at 250-400mm, but this is with the Rokinon 85mm f/1.4 which makes it a bit more fun to see an object “in context”, especially something large like M31.

I didn’t take pictures of the imaging rig, but I should have. The 55 sub-frames were taken with two different cameras simultaneously, mounted on a SkyWatcher AZ-GTi in equatorial mode, and untracked (equipment problems, I gave up on tracking). From my earlier post, you might realize that the individual frames had some issues, but the final result came out pretty good, especially when down-sampled for the web, like here.

The mount was set to dither, so the fixed-pattern noise that plagued my images from 2020 is gone. But in addition, using a second camera means there are two different patterns which further cleans it up. I also think that some of the aberrations from the lens that show up in a single frame get averaged out with the two camera setup, especially since the cameras are mounted in opposite orientations.

The cameras were dual-mounted on the SkyWatch AZ-GTi, but rotated on their sides. That means north was to the top of the frame in one, and to the bottom in the other. That probably makes no difference in the noise patterns, but… it also means that physical up is in opposite directions relative to the camera, so any lens droop in one camera is rotated 180° compared to the other. The stacking and rejection process might help there. Or maybe I’m fooling myself about the cause, but the aberrations seem absent in the final stack.