I'm curious to compare experiences with others shooting the night sky with medium format equipment. I previously did a couple of test shots with an IQ-260 but I'm now using the IQ-3100. My goal is to be able to print crystal clear, noise free images up to 48 inches across.
I've experimented with three approaches:
1: ISO 1600 for 30 seconds @ f/4.0
2: ISO 1600 for 30 seconds @ f/4.0 with tracking and image stacking in Photoshop
3: ISO 400 for 4 minutes @ f/4.0 with tracking
Of the three, option #3 gives me the best results, but is the most cumbersome to use. Each exposure take 8 minutes, you have to photograph the foreground separately without tracking, and you have to have a good view of the North Star for best alignment. The length of the exposure time also makes stitched panoramas much more challenging so I have not explored that yet.
I'm using the Sky-Watcher Star Adventurer tracking mount along with the optional equatorial mount. I chose it because it offers an 11 pound payload capacity and has an integral alignment scope. I've not had any problems with it handling the XF / IQ-3100 with the 35mm LS lens, even when it's mounted as shown, though this position puts a lot of torque on the mount and it does sag a little. I'm planning to buy or make an angle bracket to position the camera more on top of the unit. The only real drawback I've found is that the alignment scope is built into the central axis of the mount so you have to align the mount before you mount the camera. If anything shifts then you have to remove the camera and ballhead to re-align the setup. I haven't tried tracking longer than 4 minutes, but I've had very good results at 4 minutes.
I've used the P1 28mm FP, 35mm LS and 150mm LS lens. The 28mm is noticeably better than the 28mm, especially as far as chromatic and coma aberrations are concerned. Focus can be a challenge with any of the lenses since they don't have a hard stop exactly at infinity.
I'm still very undecided about post processing. Nearly all Milky Way photos I see online have been processed very heavily to really bring out the galactic center. They're dramatic, but not representative of what you actually see. On the other hand, the purpose of photography is to show what you cannot see, so maybe that's OK too.
It also seems that the "right" amount of processing to boost contrast and saturation varies with the target resolution and print size. Smaller and lower resolution images seem to need more processing. When the tracking mount is set up correctly the stars are all rendered as pin points of light, so it seems to take more of a contrast boost to bring them out, especially at lower resolution usage. With non-tracked exposures the short star trail helps to highlight the stars at low resolution, but they definitely show streaks when enlarged.
I've mostly just done test shots near home, but I'll be leaving in a couple of days for the Western US and hope to do some more serious night photography.
I'm curious what approaches others are using and what we can learn from each other.