Suggestions for wide-angle lens for Canon 40D

20/2.8 is wide only on a full-frame body. On a 40D the field-of-view is similar to a 35 mm lens, just short of normal.

For landscape, what you want is a lens that does 10 mm or 11 mm. Have a look at Canon 10-22, Sigma 10-20, Tokina 11-16. Tamron 10-24 should be out soon. All of these ultrawides are sharp and will mate nicely with your 24- 105. Can't go wrong.

(1) How does this compare it with an L-series?

Depends on which L lens you are talking about. The EF 20mm is exceptionally prone to flare, a tiny bit "soft" wide open and generally not that exciting optically. However, it makes a nice moderate wide angle lens and I like its perspective and overall characteristics (f/2.8, weight, USM, no distracting distortion) a lot. It is a nice carry-around lens for casual wide angle photography.

(2) Any chance a wide angle converter might work better with my existing 24-105 lens?

Wide angle converters are very poor optically compared to dedicated wide angle lenses. I didn't know they where making one for the EF 24-105mm, but I doubt that it will be equal to the EF 20mm in any way.

(3) Should I simply spend the extra $220 and get the 17-40mm f/4L USM instead?

Optically this L zoom is pretty much the same as the EF 20mm -- decent, but not outstanding, with a little less flare and a tiny bit more "softness" wide open. You lose one stop, though, and have a heavier and more front-heavy lens. It is still not very wide on a crop-factor body. If you want to go wide, better choose any of them super-wide zooms the various manufacturers offer -- they are all better than the old EF 17-40mm and EF 20mm lenses and give you a much bigger angle-of-view.

I love my Canon 10-22 ultra-wide zoom, which would work fine on the 40D. Quite contrasty and sharp. Only downsides: (i) it's not cheap, and (ii) it's not so great indoors in low-light. Outdoors, it's tops.

17-40 f/4L USM

I shoot over 50% of my photos with the 40D + EF 16-35 lens. HIGHLY/Top recommended.

I love my 16-35mmf2.8 lens on my 30D. It's my first L lens and so far my favorite. I agonized over the different wide angles available and haven't regretted it once. Except when I took a look at the bill but it was only for a few seconds.

I would go after the 17-55 2.8 IS. I love the lens and it works great in or out. The 10-22 is fun lens too but to keep it sharp, you need to crank it down a bit. Outside/good lighting the lens is fun and it's wide! My work horse are either the 17-55 2.8 or 24-105.

Hands down - the Tokina 11-16 2.8 The issue is that it's hard to find. Take a look at reviews, and you won't find a move beloved lens that this baby. It's consistent 2.8 through the range, is ultra sharp, and will work on full frame if you can stand a little vignetting. I love this lens. It gives me those shots no one else can get, and I've never heard anything but love for it. hope you can find it somewhere. Turned out my local camera shop had one, but they are hard to find.

Let us know what you pick!

I have a 40D and just got the 10/22mm so far I like the lens a lot. it might not be a 2.8 but it that does not bother me a whole lot. I also used a 17-55 2.8 for a week and absolutely love that lens (next in my list) 2.8 all the way, IS, very sharp and great contrast. Aside from the $1000 price tag everything else apeals to me. Seems also like you need to resolve is how wide do you want to go once you consider the 1.6 crop and if you want a zoom or a fix prime loke the EF 14mm F/2.8 II USM. Good luck Alex