Cor, what a frustrating evening! I finally got the modified lens adaptor back last Saturday allowing me to fit a medium format 165mm focal length f/2.8 Pentax lens in front of my new CCD camera. Tonight was clear, in a rather hazy way, so I started manually focussing via a series of 10 second exposures through a green filter. Just as I was closing in on a good setting the clouds rolled in. About an hour later the stars were back but sky transparency was pretty rubbish but at least I was able to complete focussing. Now for the serious imaging, thought I. Wrong!!!
I had MaximDL controlling the telescope mount as well as the camera and filter wheel and I had a preprogrammed sequence of shots set up. The first was one of an intended three 1000 second exposures through the Hα filter but at the end of that exposure when it downloaded two things happened. First I got a nasty shock because the stars were horribly bloated and then MaximDL gave me a rude message about my not having told it what the focal length of the "telescope" was and it summarily aborted the sequence. Doh, it might have told me it needed more information earlier and it was doubly frustrating as it already knew the field of view of the camera, that information having been entered elsewhere. It uses the information to command a small dither (a few pixels) between shots so that CCD defects may more easily be detected and removed during subsequent processing. For the record I had hoped, in addition to three 1000 second Hα shots and the same number of "darks" to take three sets of 200 second "lights" through each of my red, green and blue filters and, of course, the matching darks to go with them.
The star bloat and lack of fine detail in the emission nebula was simple enough to explain - the lens had dewed up.
2 inch dew heater (0.3 amp current draw) is now on order. Crazy game as the camera sucks up to 5 amps to power its Peltier cooler but the heat produced gets wasted rather than being directed towards the other end of the imaging train to keep the optics dew free. Hmm, Heath-Robinson would be reaching for lengths of flexible tubing and a small computer case fan at this point...
Anyway, with the Moon rising well above the horizon I decided to call it quits. Here is the single exposure I took through the Hα filter. It's effectively unprocessed apart from stretching, levels etc as the underlying quality is so poor that it just isn't worth doing the darks, bias and flats stuff. It's a shame because I can see that there's a lot more to come once I get some good data, and a "dry" lens, but I offer it here to show the awesome field of view the 165mm lens plus 52.1 mm diagonal sensor provide.
The original is 4096x4096 pixels but I've downsized it to 512x512 pixels for display on the forum. The best focus test shot, a 10 second exposure through a green filter and complete with hot pixels and also effectively unprocessed is available here
(616 kB JPEG) at full 4096x4096 pixel resolution for those who want to take a look. Stars are sharp in the centre (Deneb is the bright one near the centre) but exhibit some coma, particularly at the extreme top left and bottom right corners.