I just switched from Nikon, and I'm looking into rebuilding my lens collection. A 70-200 2.8 is coming in as we type, and a fifty of some sort is also taking place in the bag. That leaves me with the wide angle stuff. I'm now shooting on a 1D mark iv body, and I find it hard to find a decent wide angle lens given the 1.3 crop. I don't need to go wider than 24mm, but I would like to.
I shoot a lot of surfing, and I need to be able to attach a filter on the lens (excludes sigma 12-24mm, canon 14mm). I also need a lens that is good at handling CA and has quick focusing. Cost is not a big concern. I'm eyeing 17-40, 16-35 and the 24mm. What route to go?
Even with full frame and no crop factor, 24mm is a good wide angle focal length, but it's not extremely wide (equal to 15mm on a 1.6x crop camera, and 19.5mm on your 1.3x crop). I'm considering the Rokinon 14mm f/2.8, as for the money (a good price is under $300) there just is nothing else. Read the reviews of it, you'll be surprised. Yes it's manual focus and aperture setting, but at this wide focal length, that is manageable much of the time. A friend of mine has the Tokina 16-28, it appears to be very good for the price...but the reviews say it is notorious for having decentering issues...and also it has a bit of strange flare, which is very likely related to coma. From the images I've seen online, the Rokinon has extremely low to almost non-existent coma, even wide open. The Canon 17-40 is really the only other wide angle lens that appears to be a good value. At 17mm the tests I've seen, are not great, but it's usable if closed down a lot. The Zeiss 18mm f/3.5, is probably the next best value in wide angle lenses, especially if you can get one discounted or used, but still in good condtion. But this will still cost around $900 to $1000, used. It easily has the best color and contrast of all the others I mention above...but it's also not exactly sharp wide open...and is still manual focus. But aperture is set in camera, a plus. It's a shame Sigma hasn't made an "art" wide angle lens yet, will probably be a year or two, it seems...if at all. I have my Sigma 24mm f/1.8 for sale now. It's not perfect, but it's a very unique lens with very low barrel distortion, autofocuses well...and my asking price is not much higher than the Rokinon 14mm. If 35mm is wide enough for you, then both Sigma and Canon have very good f/1.4 lenses at that length.