Here is a 30-second shot at 1600 ASA of Arcturus, this time no noise reduction enabled, and parameter settings cleared. In getting into focus, it struck me how crisp the diffraction lines were - like sabers. This is likely not perfect focus as the visual acuity of this new scope clearly exceeds the limits of my 8 MP camera. When they say the AT6RC is an astrograph, they're not kidding. Be forewarned, the AT6RC is not intended for visual observing. Both of the 2" extensions were necessary to achieve prime focus with the DSLR. Evaluating image with eyepiece required a barlow and extension...looked like a damn microscope mounted on the back of the telescope. Very glad I added the 60mm short, great for viewing and with a 2" compression adapter I'll play with the camera use on it, too.
After this I took several 30-second shots of M4 before clouds set in, so I could get some feel as to overall improvement on a short collection of exposures. Found that stars were consistently spherical. Still picked up perceptible tracking error at 30 seconds (expected), and I did notice coma in the lower left and part of lower center in the overall image. This suggests I need to check collimation. The coma is certainly no where near as bad as on the Newt. I'm really just being nit picky. The image is excellent.
Unfortunately, my attention was diverted by the increased amp glow captured in so little frames. Yikes. I mentioned in prior posts the increasing strength of the glow. It would seem reasonable to deduce that over time taking the length of exposures required for astrophotography are pushing the limits of this camera design. The battery unit and power supply are just too close and the sensor is not well isolated from the energy produced - the amp glow is "burning in" to the sensor.
For the record, this is the 10,152nd exposure taken with the Rebel XT. Guess, it is time for a new camera. Supposedly, the new Rebel designs have improved noise reduction and have eliminated amp glow. Therefore, I should get considerably much more life out of a new camera. The XT will work just fine consigned to normal day photography, and I have a lovely lens kit for it.
A little pricey, but I've decided to purchase the new Rebel T1i (body-only of, course). It jumps two generations in DIGIC processor technology, almost doubles the image density to 15.1 megapixels, doubles my gain to 3200 ASA, and includes HD movie capture. Curiously, the movie capture mode suggests I could take planetary images like the current webcam craze...with way better resolution.
Ok. I done spending money, now.