Well that's just wacky! :-). Just to be clear, when you say you see these on every sub, are you referring to calibrated subs or raw subs?
And to reiterate, it looks nothing like any frost I've seen, and I've seen quite a bit. If this occurred on your raw subs, but didn't occur on your flats, then it's got to be a camera issue. Hopefully a transient one.
I'd try shooting some more lights and see if you still get it. Try to recreate the same conditions for exposure length, gain, and temperature. You could also try some lights in very different conditions, like during the day at a distant target. Those tests might give you some insight.
I've looked at both the raw subs and the calibrated subs and the dark spots are on both. The spots are not as prominent on the subs, but they are clearly noticeable. The dark spots don't change shape or move from the first sub to the last sub so I don't think it's frost or dew (it might be, but I don't think so).
I'm going to try some exposures during the day and see what happens.
Tonight is going to be the only clear night for the next week (at least), so I'm going to dedicate the evening to testing.
I'm thinking the cause is either a defective camera (possible, but unlikely) or user error (tremendously likely).
What are the acq parameters? Gain, and offset? Maybe share a link to some un-touched lights/subframes?
I don't know what acq parameters are? I'm still very new to this. I'm happy to share. What are acq paramters?
Gain and offset. I THINK this might be the issue, because the reality is I don't truly understand the exposure concept. I've read a LOT and I can recite the definitions. But I really don't understand the implications, nor how to apply the concepts to set the "right" exposure.
Currently, my gain is at 96 and my offset is at 20. These values come from the results of a Sharpcap image analysis. Because I don't REALLY know how to best set my exposure, I went with a "cookbook" approach and just took the analysis results.
According to the Sharpcap results, 96 is where my camera is at unity gain.
I've read a LOT of conflicting information about the offset setting for this camera (ASI071 MC Pro). I read this thread: https://www.cloudyni...ro-cmos-offset/
It looks like offset settings have changed with a driver change. There used to be 3 recommended offset values, then the offset option was removed, then the native driver was updated and the offset adjustment option was returned.
Last night I took a look at examples of all my subs over the last month (when I started this amazing hobby). Here's what I noticed:
- Until this past Saturday, my images are at 119s and 20 offset for exposure.
- I've been using the ZWO duoband filter to help combat really bad light pollution (I'm in a bortle 6 zone, but I have two street lights in very close proximity the cause me no end of trouble)
- In my earlier subs (all at 119s) I THINK i can see these dark spots. They might be there, but they might not. In my earlier subs, if they even exist there, they seem to be part of the background.
- This set of subs (from this past Saturday) is my first attempt at 300s exposure (still with a 20 offset). Obviously, these spots are VERY prominent.
- Looking at the stacked image that started this thread, the vast majority of dark spots have no stars in the background. A few do have a star or two in the background, but these dark spots seem to be primarily in a dark spot of the sky.
I THINK the dark spots may be the result of too low an offset. With the offset at 20, there just isn't very much light in the well. Using the duoband filter restricts a lot of light from hitting the sensor. If these dark areas on my image don't get many photons (and result in producing very low signal) AND my offset is low I'm thinking this will produce a dark spot that gets exacerbated by stacking. I DO dither after every shot which is why some of the dark spots have a star or two in the background, but the generalized "roundish" shape of the dark spots is likely due to the dither moving around a dark area that has a low offset.
Tonight I plan to shoot 300s exposures with the duoband filter. I'm going to shoot 2 or 3 images at 20 offset, then switch to 65 offset and see what those 2 or 3 images look like. Then, I'll remove the duoband filter from the light path and see what those images look like at 20 and 65 offset.
Those of you who have a MC071 Pro and shoot in relatively poor light conditions, how do you set your exposure?