The above image of M76 was the first taken with the GuideDog Starmaster beta. The image is made from a Normalized Median combination of 11 one-minute exposures at ISO 1600 using a Canon 10 digital SLR. IMAGES PLUS and NEAT IMAGE were used for image processing. The image was taken on 10/03/04 with a rising Moon. M76 was nearing zenith where field rotation was becoming a big problem. This was test image taken to determine if the beta of GuideDog would work and adjustments were made to GuideDog parameters during the acquisition of exposures. The image is nearly full frame with some minor cropping of two edges after the stacking process.
My scope was not well balanced in altitude so tracking was not good in that direction. Below is a one-minute raw image that shows the extent of the tracking errors with no guide corrections:
UNGUIDED one-minute exposure:
Because of the tracking errors being experienced on M76, it was a good test to see how well GuideDog could handle the corrections needed. My 20 inch Starmaster that I was imaging through is 2300mm focal length. The 102mm guidescope is 500mm. I was using a philips TouCam webcam in the guidescope with a 3X barlow so I entered 1500mm as the Guidescope focal length in GuideDog. It would have been better for guide corrections to use a 5X powermate instead of the 3X barlow, which would have provided a Guidescope focal length of 2500mm.
During the guide corrections, I made adjustments in GudeDog for the settings of RA Guide Rate and DEC Guide Rate. Since the new Skytracker guide rate was set up by Victor to be 7 arcseconds/second, I used that value and also tried 6 and 8 arcseconds/second. I also tried adjustments to GuideDog's "aggressiveness" setting all in the attempt to reduce guide errors. During these adjustments, the one-minute images being captured by the 10D and transferred to my notebook, showed the effects of the changes I was making to the GuideDog settings during imaging. GuideDog has the parameters needed to fine tune the autoguiding for making optimum guide corrections.
Conclusion:
I was very pleased with my first time out autoguiding with GuideDog on the Starmaster. It was a great feeling to be able to click the "GUIDE" button in GuideDog and watch the program do its work in making precise guide corrections to the large dob. Sure beats the manual guiding I had done in the past with a reticle eyepiece. Next time out I plan to guide with the 5X powermate. I will also measure the actual guide rate of the SkyTracker to confirm that the actual rate is the design rate of 7 arcseconds/second in both altitude and right ascension. I plan to select objects for imaging that are located in the parts of the night sky that will allow image exposures of two to four minutes without field rotation for stacking.
Many thanks for the hard work of Steve Barkes and perseverance of Victor McKeighan for making autoguiding of the Starmaster possible.
Gary Honis