Grey gave you some great advice on forums and Backyard EOS is _very_ popular (only runs on Windows). I primarily use a Mac and have just started using a program called Nebulosity ... not exactly the same as Backyard EOS but it has many similarities. AP work is divided into your skill for "image capture" and then skills for "image processing". The guys who post amazing AP photos are good at both. I'm still working on "image capture".
I use a 60Da for astrophotography -- that's the only body Canon makes specific for AP. They made a 20Da years ago. Many people will use any Rebel body for astrophotography and these can either be unmodified or modified (warning: modification voids warranty -- not for the timid -- don't do this if you can't afford to break your camera and be ok with that.)
90% of all "normal" matter in the universe are hydrogen atoms. That means there are many nebula emitting light dominantly following the Ballmer series for Hydrogen emission lines. The strongest of these is the hydrogen alpha line at about 656nm (which shows up as a rich blood red color.) The visible spectrum for humans is roughly 400nm (violet) up to 700nm (red). Above 700nm is the near infrared. So the Ha line at 656 is solidly inside the visible spectrum. The "problem" with digital cameras is that they all need to filter out both UV and IR light because the sensor would be sensitive to those. Each unique wavelength focuses at a slightly different distance -- when you start allowing UV and IR light to pass, you start getting "fringing" around things that should otherwise be sharp. By blocking those wavelengths you get a sharper image.
But traditional cameras start blocking IR beginning at around 600nm ... WELL inside the visible spectrum. It cuts reds quite a bit (much more than most people would guess.)
The 60Da has a much better IR filter (it still has a filter) which doesn't block much of anything until it gets safely past the Ha line. This allows the camera to collect about 3x more Ha than an unmodified DSLR -- which makes for better light collection and shorter exposures. Shorter exposures means less noise and less time for something to go wrong with tracking.
The exposure times in AP will be long enough that you will want Canon's AC power adapter (a good AP session will kill a fully charged battery before you're done.) The 60Da includes the adapter. It also includes an adapter cable that allows you to use the Canon TC-80N3 intervalometer with the 60Da (the connection is different.) It does not include a TC-80N3... but if you use a computer and a program like Backyard EOS then you wouldn't need a TC-80N3... you'd just need an extra long USB cable and the computer will control everything.
You can modify a camera body either by removing the factory filter and installing a better filter -or- you can just remove the filter and replace it with a clear "filter" (which isn't really filtering anything but serves to protect the sensor and also the low-pass filter on the camera is part of the piezoelectric dust-cleaning system so the replacement is also a dust protector.) If you have no filter at all then you must use external filters (which most astrophotographers are happy to do.)
The Gary Honis website discusses modification of various Rebel bodies and how to do it (warning: this WILL void your warranty... this will likley become obvious as you start reading and looking at photos of how this is done, but I thought it bears repeating.) Google for "Gary Honis" to find his site.
Tim Campbell
5D III, 5D IV, 60Da
