Re: Lens confusion
Unfortunately this can turn into one of those "you get what you pay for" situations...
For widefield work on a Canon APS-C camera the EFS17-55 IS F2.8 is hard to beat. This is a (relatively) expensive, fast, heavy, L-quality optics lens that is great for astro work. If I could only buy 1 APS-C astro lens it would be this one as it is top quality and flexible. This lens won't work on full-frame professional cameras like the 5D or 1D...
The 70-200 F4L is also a great lens. It is a lot lighter (but one stop slower) than the F2.8 version. It can be used with a Canon converter (expensive) to become a very good 280 or 400mm f5.6 (at which point you are into small refractor territory IMO). Remember these Canon lenses are top quality with superb coatings and optics. Their image quality is much higher than the kit lenses - as is their price!. They are also superb when used for serious terrestrial photography - which is why Pro's use them. The 70-200 F4 L is a great bargain right now as everyone wants the IS version for terrestrial sports/nature work so the non-IS version (same optics) can be picked up relatively cheaply. As stated earlier, you don't need IS for tripod/astro work - it needs to be turned OFF.
Other "widefield" bargains are the 50mm f1.8 (aka "nifty fifty") which has great optics for the price (although build quality is "basic") and the 28mm F1.8 which is a top quality item at a reasonable price. I use this latter lens as my standard indoor low light/high ISO/no flash lens on my 7D - it takes great portraits.
Don't forget with an APS-C camera to multiply all of the focal length numbers above by the 1.6 "crop factor"...
Telescope:Equinox ED80 Pro (Schott/Ohara Fluorite) with Baader Steeltrack + Nexstar 6SE OTA
Mount: Skywatcher HEQ5 Pro+EQDIR Camera: JTW 1100D Ultimate V3 (on order), Astronomik Clip filters, Samsung SCB-4000, IS DBK21AU618.AS
Accessories: Baader 8-24 MkIII, Ortho 5mm, Aspheric 31mm, Meade 12mm reticule, Televue Powermate 2.5x, BAST Motorfocus+FCUSB, Skywatcher Field Flattener, Orion RACI, Orion Mag Mini/SSAG, Canon IS 15x50 Bins
Software: EQMOD/Stellarium/Registax/BackyardEOS/PixInsight,PHD,AlignMaster, AstroTortilla