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One other point about CCD cameras that is worth mentioning.
Most of the modern cameras have their firmware on an internal flash memory. The SBI STX does but the ST series and STL series does not. I think Starlight express does as well and not sure about Atik or QHY.
What that means is the drivers are loaded into the camera from the computer and it takes a little while to do that. If the power gets interrupted (which happens very often with my ST402 as it has a cheap and weak power jack - this reminds me I need to replace that jack) then
you will get an error message when you go to take an image.
Reconnecting the power will not reconnect it in the software. You have to close down CCDsoft and reopen after you have repowered the camera. Wait the 25 seconds or so for it to load the drivers and then reconnect. This means losing your cooling etc. and autoguiding and restarting everything. OK, if everything is working well it probably would not happen that often but it is surprising how often it can still occur.
Modern cameras have the drivers in the camera. My Apogee and FLI cameras and Starlight Express cameras connect instantly. The SBIG takes about 20 odd seconds and sometimes fails. The others almost never. Also you can unplug the Apogee and FLI camera and plug it back into the computer and it is still running at the same temperature and ready to go. NICE. Especially at 3am when you are tired and cold. A lot less swearing!
The other consideration is download times. Slow download times mean the autoguider stops when the download is in progress and the tracking errors build up. If you started another exposure straight away you would be starting at maximum guide errors which then reduce over the first 20-30 seconds of the image. So you have to program in a delay before the next imag starts. FLI was fastest with 1 second downloads with a 1x1 binned image - lightning. Apogee wasn't too bad. I see QSI series 600 has the same download speeds now as FLI - excellent. Also they have -45C ambient cooldown. Plus with the fast downloads, the drivers on board, the off axis guiders, the internal filter wheel means I think they have now overtaken FLI in practicality. FLI have some other nice features not sure QSI matches like antireflection coatings on quartz CCD windows, sealed chambers with inert gas that do not need desiccants etc and the option of no cover slip which gains a bit of extra QE and less halos.
The only thing they haven't gotten now is ghost image control. That is called RBI (residual bulk image). That means if you shoot flats at dusk then the chip will retain some of the charge in the deep layers of the silicone. It slowly leaks out during the later exposures meaning your darks will not match the lights 100%. All full frame KAF series chips do this. Some worse than others. The 09000 chip I believe is the worst. Without RBI control you would have great diffifculty in using a 09000 chip.
I have used several KAF chips and I can't say that this has affected my images or if it has I am unaware of its effects. My FLI camera has the ability to handle this by an infrared flash of the sensor before it takes a light. You take your darks also preflashed in IR and you can control how much it is preflashed. Now your darks and lights are matched more exactly. Richard Crisp has written a paper about this with examples and he is a leading exponent of this technology. Apogee also have RBI control. I don't think any of the others do. Again I am not sure how much difference you would see in your images from this effect. I should try it out to see for myself if it is worth the trouble.
Another aspect of course is weight. Lighter is better. FLI Microline is light, Apogee Alta is medium to heavy, Apogee Ascent would be light, Starlight Express would be light, SBIG 8300 light, SBIG STL medium.
As far as QHY and Atik goes I know nothing so I can't comment.
They are up and coming makers. I had a little Atik camera once which was a cheap ToUcam type camera so they have come a long way.
There is another new maker called Morovian. Again, I know nothing about them. But the above and preceding principles still apply.
Greg.
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