refractor obtained a few months ago. The task for Saturday was to get the auto-guider working with the AP1200 mounting. I always try to keep things as simple as possible out in the field, and the use of any auto-guider means using a computer - believe it or not, new for me as it requires a power beyond a 12 volt battery... Melinda and I got a little portable notebook computer a couple years back that hasn't found a permanent application, so was going to try to run new software and hardware on a relatively new mount and scope - what could go wrong?!
Nearly all telescope drives have slop, periodic and alignment errors that limit tracking accuracy. In the past, macho astronomer that I am, I'd normally guide manually when it was needed. The image at left shows the little auto-guider I first used with Pat's setup in June. Even with a scope so much smaller than the one shooting through, small pixels in the compact cameras and sophisticated software work at keeping the tracking nearly perfect for long exposures.
And let me talk about digital cameras for a
minute. Virtually all of the images taken in the 800+ posts here are taken with couple Canon DSLRs that I own. Compared to olden days using film these newer cameras are a godsend! No waiting for processing to find out the telescope or lens was out of focus, or poorly tracked, or object decentered. The digital images go immediately in the telescope for stacking or further processing. There are issues though - consumer cameras work great for most applications, but for long exposures, electronic noise is added to the signal. Specialized astronomy cameras are cooled to reduce noise, separate dark exposures can be taken to minimize the noise, and many exposures can be averaged to reduce noise compared to the faint signals. The exposures shown here were taken Saturday at Pat's. At left is a full-resolution partial frame of Messier 20. It is a 3.5 minute exposure with the TEC 140. The red, green and blue speckles are actually "hot pixels" where some of the little sensors have more noise than others. Fortunately, they mostly repeat really well, so darks can be taken separately, like at left. This is the exact same piece of the sensor, so the hot pixels repeat in both images. Check out the green clump of them above center. The "dark" is typically subtracted to reduce noise in the object's image.
It was a fun night - Pat helped me with some guider stuff, and I helped him with some collimation issues, so we both benefited by our company. We'll likely do it again soon...