Telescope Reviews: Water Pump for STL 11000

You don't say what your night time temperatures are. The camera comfortably cools about 35C below ambient, if that gets down to -15C, 20C ambient, then you probably don't want to bother with water cooling and all that entails. Even at 25C ambient some nights I doubt I'd bother with it. But if 25C and warmer is common then it likely would be worth the effort as you'll need fewer exposures to achieve the same noise level in the final image. Sky brightness however can make this moot. I'm talking very dark skies. Brighter skies mask the noise to some extent, both the heat and system type noise can be lost in sky noise. To what extent depends on your background levels.

Much has been said here on water cooling, pump selection, water management, etc. Search the archives and you'll turn up a lot on the subject.

My experience has been that once cooled to -15C the gain from going colder is very small if you have a good dark library, 25 or so, taken at the same time and temperature. The library lasts 6 months or longer and well worth the effort. I standardize my temperatures at -15, -25, -35 and -45C and exposure times at 10 minutes for LRGB and 30 for narrowband. This means I can shoot darks a few cloudy nights while I sleep and am set for the next 6 months. Once Median or Sigma combined you can discard the individual frames. Take your lights using dithering using auto dark and flat calibration as they are taken then align and median or better sigma combine 6 or more and you will not be able to tell which were shot at what temperature. If I use only 4 lights and thus must use average combine then I can just barely detect the -15C images but the cooler ones are exactly the same. At -5C I needed twice the frames to get the same noise level as at -15C however so there water cooling might be useful if needed to get colder. You might wonder why I use -35 and -45C if there's no difference. That's because in winter my ambient temperature is always below -25C and often below -35C. Even at those temperatures you want well temperature regulated images for best noise reduction so I'm forced to use those temperatures. But stay as "warm" as possible as frosting of the CCD window's outside surface can occur at such low temperatures. Also avoid binned exposures if below -30C ambient as that can cause blooms that run to the right (not down as you'd expect). The camera is certified only to -30C ambient so going below does something to the timing circuits that cause the bloom. While it can happen even at 1x1 its rare there and if a problem there's a service page on the SBIG website on how to adjust a pot to eliminate it. If your night temperatures never get this low then it isn't a problem.

Rick