Tuesday, January 17, 2012

Cold Weather Performance

Tonight I'm shooting O-III frames of the NGC 2244 (the Rosette Nebula) to add to those already taken the other night. Tonight will probably be the coldest night we've had so far this winter, which is not really saying much.  The next couple of nights we will probably go below zero for the first time this winter.  It's hard to believe this is Minnesota! Oh, and there's just a trace of snow on the ground. Really strange.

How well does everything run at 9° F (-13° C, the current temperature on our screened porch)?

  • Gateway Laptop
  • ST-8300M (which I'm running at -30° C just to match existing dark frames
  • Extension cord from house (it's one of those low temperature cords, highly recommended. (Note added: at 5° F the cord began to stiffen a little, but it was still easy to coil for storage.)
  • AT72ED, focuser remains smooth (Note added: at 5° F the focuser became rather resistant to change, as if the lubricant were solidifying or parts were tightening because of differential contraction.)
Less than perfectly, but passable:
  • Me
  • Cables (all are very stiff)

Not very well:
  • SBIG filter wheel.  (reports an error when moving from filter to filter, but gets there okay. I've noticed that temperatures in the teens or lower cause this behavior. Maybe these are built for the weather in Santa Barbara?)
  • CGEM mount. It looks like the mount is moving in fits and starts, elongating the stars in right ascension. I can't yet tell if this is periodic motion that can eventually be eradicated. It might well be something else, perhaps caused by the stiffening of lubricant? I tried to change the balance in RA, but that didn't help. Most of my images from the evening have very elongated stars. Maybe I can compensate by using the Ha image as luminosity and red, the OIII as blue and the SII as green?  Time to experiment!
It's perfectly clear tonight, with just the lightest breeze; by the end of imaging at midnight, the temperature had fallen to 5° F (-15° C). The poor CGEM simply couldn't track correctly in RA with the temperature in the single digits F. I'll have to look into this, as winter evenings around here are typically near that range.

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