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The method I use for attaching my camera directly to my HEQ5 mount can be seen here, with photos: http://grelf.net/piggy-back.html#N656258
Please read the rest of my site because I have put lots of hints and tips like that on it. There is also my book, aimed at photographers: http://www.ypdbooks.com/photography/1050-the-dark-skies-of-the-north-pennines-YPD00983.html
David,
I suggest you should get the most recent model you can afford, because they continually get better. Since 2001 I have traded up through 5 Canon DSLRs and each has been better in terms of increased sensitivity and yet less noise (analogous to grain on film). So 1200D in preference to 1100D or 1000D.
I concentrate on deep sky and comet photography. So I would go instead for the 100D because it has the highest native sensitivity, at ISO 12800 (the 1200D only goes up to ISO 6400). By native I mean amplifying before digitisation rather by software afterwards (which would be counter-productive for astrophotography). Although the 100D series is considered to be at a higher level than the 1000D series, the 100D costs only about £50 more than the 1200D.
In the good old days of film single long exposures were the only possibility and so very accurate drives and guiding systems were required. Digital cameras enable a completely different approach, needing no guiding. Instead use the highest native (non-menu) ISO setting (in my case ISO 6400). Take many (50 or more) exposures, each of about 30 seconds to 1 minute. As Martin said, that length of exposure should be safe against trailing without guiding on a reasonable equatorial mount driving nominally at sidereal rate (I use a basic HEQ5 with the camera either using its own lens or at the prime focus of a 10″ aperture f/4.8 Newtonian). Take as many exposures as possible, to reduce the noise. Total exposure time is what matters, regardless of whether that is 1 frame or a stack of many. Then stack and post-process using free software.
There are many benefits to stacking, beyond the obvious ones, some of which I cover here: http://www.grelf.net/defects.html
