5/6/2010. I wonder if I need to work out a barlowed arrangement behind the ST80. 400mm may not be enough FL when guiding at FL's much longer than the A-P's native 762mm. A shorty barlow in the diagonal comes to focus at a reasonable extension (and reveals all kinds of dreadful issues in the ST80's images). After guiding issues are sorted out, it'll be worth trying. I experimented some with the barlow I had been using for collimating the 16-inch; it lacked a set screw for an eyepiece. I drilled and tapped a hole for a 10-24 socket screw.
I used Venus in the daylight sky as a focus target for the barlowed guidescope, took a break for lunch, and went out later to take another look. The drive and keypad were dead. Cause for alarm but not for panic: It appears that too much heat and direct sunlight can trip the overheating protection in the power supply. Or so I hope. Today is severe clear and >88°F. The power supply was uncomfortably hot to touch. I recalibrated, parked and covered the telescope and mount using the battery pack (a first, works great) and put the Pyramid power supply and its Tupperware carrier under a lawn chair to cool.
Later that same day, the power supply was fine. But since I already had the battery out, I opted to use it for tonight's photos. Amy got home from GED graduation just before astronomical twilight ready for a "midnight" snack. In the 8 minutes a frozen pizza took to cook, I uncovered the telescope, powered it up from the battery, verified approximate polar alignment, slewed to Arcturus, recalibrated, mounted the camera, focussed using liveview, slewed to M3 and powered down. After pizza, I resumed from park, slewed back to M3, centered the same magnitude 6.3 guide star I've been using for M3 (that's the bright one in the photo above), calibrated the guider according to yesterday's plan, and began a series of 5 minute exposures (50D, ISO 1000, IDAS LPR filter, F6, behind the Maxbright diagonal). After an hour, the guider continued to show only small corrections in X and Y, so I thought "why stop now?" and left everything running a while longer.
In the end, I combined sixteen, 300s subframes (that's all of them) into an 80-minute exposure of M3. Once again, the blue and red channels of the 50D are very noisy. After applying a dark frame (layer difference) and saving as TIFF, I used Maxim DL5 to align and average the frames. After reimporting to Photoshop, I discarded B and R layers, removed the remaining horizontal banding from the G layer using Noel Carboni's actionscripts, worked its curves and levels some, and then added in the defocussed color from the original combination as provided by Maxim. At full resolution, some trailing is still evident in declination. I corrected it with layers and "darken" blend mode. The image at the top of this page (obviously) uses Noel Carboni's Star Spikes Pro to add a little sparkle and further disguise some faults. Try this again with careful polar alignment and maybe mess with the backlash parms if that doesn't produce sharp stars. Closer. Much closer!
Tonight the mount and autoguider were powered for two hours by the 12v AGM motorcycle battery. It's showing no signs of exhaustion, and in fact I'd expect many more hours than this with this light load. At a guess, the mount and guider draw no more than an amp together except when the mount is slewing; the relatively constant corrections required owing to poor polar alignment may significantly increase the load.
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