I got a belated Xmas present - my QHY600 came in and I picked it up a week ago. I've had some challenges in getting it working, but overall I'm pretty pleased with it. I'm not seeing any amp glow at 5 minute exposures binned 2x2 which is as far as I plan to push it at this point. There's some large scale fixed pattern noise, though, but QHY says that this will calibrate out and I dither every frame anyway. In particular, I'm still (see below) confused about optimal settings as the documentation is still a little sketchy (IMHO) and not well written in places. There were two challenges that needed to be overcome when I first began using it to get it working as it should.
First, you have to take an initial exposure of over 1 second to get the cooling working properly. If you don't and you just connect the camera to the computer, then the cooling will cycle around forever . I found that I could never reach -10C where I planned to image. It would get to around -4 and then warm up! Just one 10 second exposure switches the camera into a normal cooling mode. This took me a while to figure out. QHY says that they will fix this in the next driver release in their response to my post on their forum.
The second is strange behavior with regards to USB connections. At home it works properly on my desktop when connected to one USB 3 port but not to a second one on the same hub. When I connect to the "bad" port I get some skipped rows - zero values. What's even stranger (on my desktop computer) is that it works perfectly using USB 2.0 ports. I wonder if anyone else has seen this behavior. At the observatory, it would not work using the USB 3 port on my CEM120EC2, but did work when connected directly to the imaging computer and to a second computer of the same design at my desk out there. I've run my ASI1600 through the CEM120EC2 USB 3 port for quite some time with good results. So that was a surprise. Right now I have two free ports on the CEM120, it will be a shame if I can't get it to work properly without a dangling cable.
(NB--- I also shot myself in the figurative foot with the CFW3 filter wheel setup. I connected the enclosed proprietary four pin connector between the camera and CFW3 filter wheel. I also connected the USB port on the camera to the USB hub on my mount. I could not get any reasonable looking pictures at all. Then the wheel failed on me after about 30 minutes. I have a new wheel (thanks to my local astronomy store) now and I carefully read the documentation this time. With the QHY600 you ONLY connect the 4 pin connector - you do not use the USB connection at all. I post this because I may not be the last person to make this mistake.)
Where it gets confusing to me is when I try to figure out the right settings for DSO long (5 minutes) exposures. The camera documentation refers to 3 modes. The setup ASCOM GUI calls these "Photographic DSO 16 Bit", "High Gain Mode 16V" and "Extend Full Well Mode". I decided to just use the Photographic DSO (Mode 0) and took the advice in the QHY online specification section (not the manual!) and set the Gain to 26. At that gain the camera switches into some mode that lowers the read noise down to around 3e. FWD is around 27K. However, in the online charts (in the specifications section) this is referred to as "Ultra High Full Well Readout" which seems to contradict what's in the written recommendation. Since I'm binning the camera 2x2, the effective FWD is around 110K which would seem more than adequate. I could go on about this, but I'd love to hear from someone who understands it better than I do (shouldn't be that hard).
I'm also completely confused about how to set the offset. I have that down to 12 at this point and built a dark library at Mode 0, Gain 26 and Offset 12 for exposures from 1 to 5 minutes. I can't imagine going longer than that but maybe narrow band will need different settings and a different library. I arrived at 12 offset by gradually lowering the offset until the bias frames gave values of between 150 and 200 but I really don't know if that's the right approach or not. I could (?) use Offset of 6 and get bias frames with readings between 50 and 70 but I worried about some pixels being negative so I kept to 12 out of fear/ignorance.
Finally, there are two "read modes" reported in MaximDL for the camera. One is "Fast" and one is "Normal". My assumption is that Fast is just to be used for plate solving, focusing, etc and "Normal" is to be used for long exposure photography. I can't find any documentation online at the QHY site about exactly how (if at all) these relate to the modes described in the GUI.
So, the camera seems pretty darn good. Tomorrow night looks clear and I'll give it another try out at the observatory but I'd love to hear from anyone who's farther along than I am with it about their experiences and what they've discovered about optimizing the performance.
Rgrds-Ross
