A couple of days ago I managed to get my hands on a Canon 20mm f2.8 lens. It's a pretty neat lens. Not too heavy and not too much of a toy feeling to it. It's something in between. I have experimented on a couple of wide angle lenses and I must admit I have an admiration towards them. Especially when I got my full frame Canon body. When I was shooting an aps-c body my 28-135, 17mm, 18-50, were basically just regular lenses to me. I then got a Sigma 10-20mm and I was like whoaaaaaaa...this 10mm point of view (equivalent to a 16mm in full frame) was craaaaazy. I didn't really use the 20mm range of that lens, I was shooting it at the 10mm range like 98% of the time. I then made the bold move to a full frame which means that I now have access to an even wider range of wide, ultra wide, and ultra ultra wide lenses.
For around $450 to $500 you can get this brand new. The Canon 20mm f2.8 USM lens was one of the first ultra wide lenses I have used in my full frame body. By the way, ultra wide lenses for full frame are around 17mm to about 20mm. Above 20mm it becomes a wide angle lens and below 17 would be ultra ultra wide. The 20mm on an aps-c sensor body will be a 32mm lens, as the aps-c bodies have that 1.6 cropping factor for lenses which means the real range is multiplied by 1.6. A 32mm lens is still considered wide for 35mm or full frame...not as wide as a real 20 though, although it is still useful for landscapes and scenery shots.
I tried this nifty lens when I was trying to decide either to get a 20mm or something wider. I ended up with a Tokina 17mm and reviewed it here. It's not that the Tokina was better...it was just cheaper, wider, and better built than the Canon 20mm. It really doesn't matter now as I have sold the Tokina 17mm a long time ago. So After I sold my Tokina I decided to give the Canon 20mm another look. I got hold of a copy and took it out for a spin. This time I was impressed more than when I tried it the first time.
The Canon 20mm is a pretty well built lens. The barrel is plastic, the mount is metal. It uses a 72mm filter which is really easy to get, plus using a regular uv filter for it does not cause that much vignetting, which is pretty common for ultra wide angle lenses. It's light, and is not troublesome when it is attached to your neck the whole day. It does not feel like the Canon 50mm 1.8 mk2 which is Canons most plasticky lens, although it's not as sturdy feeling like the Canon 70-200 2.8 IS USM which is pretty much built like a tank with its full metal barrel. It pretty much feels really secure when you mount it on your body.
This lens is excellent for landscape photography, which I think 90% of the time users of this lens is going to use it for. The ultrasonic focusing is quick, precise and pretty much silent. Manual focusing override is supported as you can grab the focus ring when the lens locks on to your subject for focusing, which means you can tweak your focus without switching the focus switch to manual. Focusing is pretty much precise as ultrawide lenses tend to focus on anything that's in the frame. They usually have a very wide depth of field and everything pretty much is in focus.
Sharpness is pretty good for this lens. The corners are not as sharp especially when you shoot the lens wide open...although not a lot of photographers who shoot landscapes shoot at the lenses maximum aperture. For landscape shots you usually close down your lens to around f8 or more, so the 2.8 maximum aperture of this lens does not really matter. Wide angle lenses are notorious for having soft edges and this lens does have the same curse. Shoot this lens to around f4 and narrower and you'll be fine. The weird thing about this lens is that you'd have to find the sharp sweet spot of it. Once you find it, the lens gives you an unusual sharpness on that spot. Sometimes it's so sharp that I forget that I am using an ultrawide instead of a normal or macro lens.
The lens does not come with a lens hood...the lens hood to use with this lens is the Canon EW75II lens hood. It's around $30-$40 online which I think is pretty high for a lens hood. You might find a cheaper aftermarket alternative.
I have read reviews about this lens online and it's pretty much a love it or hate it lens. The first time I have used it I wasn't really impressed with it. I decided to give it another chance and I was impressed, especially after I've heard about that sweet spot thing. The only gripe I have about this lens is that it's pretty pricey at around $450-$500...if it was priced around $300-$400 I'd buy it. For around $180-$200 you can get yourself a Tokina 17mm f3.5 ATX which is better built and has its own lens hood and is a tad sharper. The Canon 20mm though is lighter, has better focusing and is easier to store because of the detachable hood. The Tokina is wider, but the Canon has manual focus override...it's really up to you.