The Starry Night, 19

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Heavily processed version of M106 through marginal skies. 5,000 seconds (83 minutes), 50D, ISO 1000, ten 500 second subframes through IDAS LPR filter. Dark and flat fields applied, images aligned and averaged in Deep Sky Stacker; the green channel (the cleanest) isolated for aggressive histogram stretch; color added from DSS output file. Spikes added by Star Spikes Pro to distract from a multitude of sins. Click here for 1280 pixel version.


5/7/2010. I took some trouble to insure that the polar alignment scope and its eyepiece come to a common focus in the same plane as the reticle. Since focussing it clumsily a few nights ago, I've noticed a lot of parallax that was making confident alignment impossible. Maybe that's a large part of the alignment and tracking issue. I shimmed the scope with three patches of Scotch tape to remove the slight looseness introducedi by focussing the telescope via its mounting threads rather than with the eyepiece.

I want the alignment telescope to work well enough to provide a really good starting point for the more rigorous polar alignment routines available in the GTOCP3 toolbox. For short focal lengths, I'd like to be able to just use the alignment 'scope and leave the rest to the guider without paying for my slovenly ways with smeared stars. Stars and reticle are both razor-sharp tonight.

I calibrated on Phecda (lower, handle side of the dipper's bowl), then slewed to M106. Perfect, of course, but I need to be more careful about centering my recalibration targets before slewing to the final field.

Then I had the devil's own time getting the LVI to lock onto the 6.3 magnitude field star near M106 (the bright star to the right above). I started prior to nautical twilight, so some difficulty isn't surprising. Not until near the end of astronomical twilight did the LVI admit that it had a star to guide on. Then it kept emitting "Star Lost" errors at odd moments, like after "setting exposure" and before calibration. In fact, after the sky got reasonably dark, after I was focussed well (3 pixels), calibrated, and tracking, I still kept getting "Star Lost" alarms. The guider would misplace the star for 4 - 6 seconds at a time, then find it again and carry on for several seconds, then report "Star Lost" again. Etc. It repeated this behavior continuously throughout tonight's exposures. It's a bit unnerving. The naked eye limit was just barely below Megrez at 3.3. This night is far from a sparkler. I would have thought that 10x500s of exposure would reveal the outer spiral arms more clearly (they're present but only with extreme and judicious stretching, especially with blue emphasis). And the guider is evidently right at the edge of its reach. I attribute both these items to a hazy, bright sky.

The tracking, however, was excellent (calibrate at 0.5, guide at 0.25, aggressiveness unchanged from last time). M106 and several NGC galaxies come through the sky fog but not enough to produce a beauteous photo. We need more exposure under darker and clearer skies. And maybe the temperature controlled CCD. Or maybe more creative processing (see above; but I could still do with 3-4x as many photons). The battery worked without any problems for three hours tonight (total so far: five hours).



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                   © 2010, David Cortner