I have gone digital only recently, and the only lens that's worth keeping from my earlier pack is a 24-105 f/4L IS USM. I think I need to buy a wider angle lens - especially for landscapes - situations that my 24-105 would have covered with the analog camera. I was considering buying the Canon Super Wide Angle EF 20mm f/2.8 USM. It seems reasonably priced, and has good reviews. Can anyone advise me on: (1) How does this compare it with an L-series? (2) Any chance a wide angle converter might work better with my existing 24-105 lens? (3) Should I simply spend the extra $220 and get the 17-40mm f/4L USM instead?