M101, the Moon, and the Viewfinder

So probably not the best choice of targets on a very wet night with a nearly full moon nearby, I admit. M101 is a huge object in the sky, but with a very low brightness. But it was there, and nothing else was really within reach with the moon where it was and my scope set up where it was. But I did learn a few things, or at least remember things that I have known for years and had set aside while I worked on other problems.

I took two short sets, since I had to execute a meridian flip after a short time. Of course, I unthinkingly flipped my camera over as well, and halfway through the motion realized that my flat frames would now be useless. But for some reason, while trying to set it back in the original position, I noticed that I had the camera set for Automatic White Balance. Now, normally, that is okay, but when shooting regular pictures, I NEVER use that setting-I always choose the proper white balance for where I am. And it seems that I've had it on AWB since I started shooting with the scope.

Now, even without light pollution, the sky is not truly black, but a ruddy brown. The AWB will try and compensate for that, and all of my galaxies have been very blue. I had assumed that that was largely due to the stretching in Photoshop, which does shift color. But with the white balance restored to the proper setting, compare the tone of these two pics-the first is blue, the second is proper.

In the second picture, a mysterious enemy has shown up again. A few weeks back, I had several sets come out with that odd vertical banding. Since it then went away, I was assuming it was an artifact from one of my reference frames. But it showed up again in the second half of the shoot. The galaxy could actually brighter in this pic, but the bands were just too dominant then.

My main suspect is light leak-especially with such a bright moon, I should have also have remembered this fact about SLR cameras. It's a small and subtle flaw, small enough that for normal uses, photographers can get away with ignoring it completely. But during long exposures, light coming in the viewfinder can actually bounce around the raised mirror and hit the film or sensor. The shots I did last night with the moon at my back were simply beautifully lit, just not the light I was after. I suspect these bands will have a similar cause. Sometimes, I will shoot my dark frames while I am putting everything away, and the scope will be sitting near the door with it's it's cover on. Sometimes I remove the camera, and shoot the darks with a body cap in place. But I will usually have some light turned on then to help me break down. I am guessing now that if I toss a piece of black fabric over the camera the problem will go away. I'll probably intentionally pollute some test frames as well just to see what that looks like.

No big copies of these pics; the session was short, and too few photons were collected. I stacked these with my earlier shots of M101, but the end result was honestly no longer acceptable to me; the color balance is too awful. So no great photographs, but a step forward, repairing my brain rather than my equipment this time.