I've used this lens both on 1.6x crop (Digital Rebel XT) and full frame (5D and EOS 3) cameras.

On the 1.6x crop, the 20mm focal length looks like 32mm. I personally find that to be a wonderful focal length for general purpose use, and the f2.8 is acceptably fast for some indoor / low-light situations.

On full-frame, the lens is amazingly wide, and can be challenging to frame an interesting picture. Nevertheless, sometimes you need the lens to be that wide, so it's great to have. On the downside, the lens loses sharpness toward the edges, and is more evident on full-frame cameras than on 1.6 crop cameras.

This lack of sharpness is not always a big deal, as the edges of a photo are usually not the focal point.

I'm overall happy with it, and when I want wide, I usually grab my 20mm over my 17-40mm zoom.

If there is one thing in this universe that is more rare than gold, it is a positive review of this particular lens. Now I don't know if I just got lucky and got a good sample. But this has been a GREAT lens for me. Sharpness is actually REALLY good. Now one of the BIG complaints of this lens is poor edge sharpness. But I have not found this to be a severe problem - especially when stopped down somewhat. And, since a lens of this focal length is more likely to be used for scenics or arcitectural use than action shots, this isn't the end of the world.

But there is more going for this lens than sharpness. Distortions are VERY low for a lens of this focal length. You are NOT going to get anything nearly as good from a zoom. Also, color saturation and contrast are EXCELLENT - FAR better than, say, an EF-S 17-85mm lens. Colors REALLY come alive with this lens compared to most zooms. And chromatic aberrations are all but non-existant.

Construction also seems to be solid on my lens. The materials seem to be of good quality. The focus ring doesn't wobble much. And nothing external actually extends during focusing. This last fact is a REAL plus in outdoor environments, since an extending element creates low pressure in the lens (which can suck in dusty air).

I really have only two complaints about this lens. One it the price, which is somewhat on the high side. I personally got mine used for less. But $400+ is kind of alot to pay for a consumer grade lens. On the other hand, price is maybe not too bad, given the good overall quality of this lens. My other complaint is vignetting at large apertures. Simply put, vignetting is VERY noticeable at f/2.8 - even on an APS-C camera. I can only imagine how it might look on a full-frame camera. In fact, the vignetting makes this lens virtually unusable at f/2.8 in many situations. Of course, this gets better when you stop the lens down. At f/4, vignetting is no longer a problem. But the fact that f/2.8 is not nearly as usable as it could be is somewhat of a downer.

Of course, much like the edge sharpness issue, this is not the end of the world. And at the end of the day, you can still take some REALLY good pictures with this lens.

This lens is just what I wanted. I could not find it at any of the local shops, and the price I was being quoted to special order it was double what I paid for this lens. I am very pleased.

The lens is okay on a 1.6 crop factor digital camera, but then it isn't particularly wide-angle (32mm field of view). I hear that it is okay on a film camera, but I have no experience. On a full-frame digital camera, it stinks....Digital cameras can be affected by the angle a lens causes light to hit the sensor, and it seems to make a difference here. The lens produces smudged, blurry images on my full-frame camera. It is okay on my Rebel XTi, but not wide enough to be impressive.

Build quality is okay, but nothing special. If you buy this despite my recommendation, spend a bit of money to get the lens hood (which doesn't come with the lens). It will help keep glare off the front element.

If you can afford it, buy one of the wide-angle L zooms instead of this lens. If you can't afford those, get a Sigma zoom (preferably the 12-24, but alternately the 15-30) instead of this lens.

I highly recommend this lens. It is sharp, fast, very accurate in focusing, and light weight. I use it primarily for landscape nature shots. There are a lot of reviews out there about a few bad 20mm's. If quality of image is vital, you should do some research. If you are an amateur who just gets a big kick out of viewing your images on a computer, this lens is perfect.

I'm a long time user of Nikon from the film days. I had 1 bad experience w/Nikon digital (a bios update ruined my camera due to bad Nikon software). I will eventually go back over the Nikon line when they get their electronics on par w/Canon. Therefore, I don't want to spend a lot of money on Canon lenses but I do want some quality. These cheaper lens are perfect for this waiting period.

The lens is okay on a 1.6 crop factor digital camera, but it isn't particularly wide-angle then (32mm field of view). I hear that it is okay on a film camera, but I have no experience. On a full-frame digital camera, it stinks....Digital cameras can be affected by the angle a lens causes light to hit the sensor, and it seems to make a difference here. The lens produces smudged, blurry images on my full-frame camera. It is okay on my Rebel XTi, but not wide enough to be impressive. It stinks on my 1Ds.

Build quality is okay, but nothing special. If you buy this despite my recommendation, spend a bit of money to get the lens hood (which doesn't come with the lens). It will help keep glare off the front element.

If you can afford it, buy one of the wide-angle L zooms instead of this lens. If you can't afford those, get a Sigma zoom (preferably the 12-24, but alternately the 15-30) instead of this lens.

I shoot both film and digital images with this lens. This lens is on my camera 80% of the time. It is a very fast and solid lens. I have not found any zoom that can compete. I love it.

The 20mm works great for those tite spaces in parties or rooms. I like it!

I wanted a 20mm prime to use for night shooting, so I thought I'd give this one a try. I chose poorly. Returned it the same day. Still on the hunt for a good prime night long exposure performer.

This lens was really soft around the edges (even on my 40D with a 1.6x FOVCF). Although I don't need a fast focusing lens for night use, this lens still focused slowly during its day use.

It's grossly overpriced. Should be only $299 at most.

I hella enjoy using this lens, its always hooked on my Canon 40d. One of Canons cheap wide lens. Excellent made, perfect.

If you want a wide-angle lens for a Rebel that doesn't have lots of distortion, this is great. I have taken some very nice shots with this hand-held indoors and outside. The first time I took a stopped-down shot indoors on a tripod, I was really impressed. Because of the crop factor and depth of field, it's eye-popping sharp all over with great color saturation. It costs a good amount, but it's one of the most useful lenses I have.

Drawbacks - A chunk of that price is for the 20mm optics of which we only see the central portion with a cropped sensor. The lens hood is extra.

This is one of the first two lenses I bought when I switched to a Canon SLR about five years ago. I've had plenty of opportunity to use it since then, both with film and (full frame) digital.

The idea behind this lens is a good one -- 20mm is wide enough to allow for landscape and architectural photos, and it focuses close enough for entertaining photos of people's faces, taken about a foot away from their noses (note that you'll need either a ring light or lucky ambient light to pull off the latter). There is some pincushion distortion, but nobody would accuse the results of looking like a funhouse mirror, as would be the case with a fisheye lens, for example.

f2.8 is fast enough; I've no complaints there. Unfortunately, this camera consistently vignettes -- the corners of every image are dim. This is true even with a bare lens, and filters make it worse. You can correct the problem in image editing software, or just crop the image, but what's the point of buying a 20mm lens if you're going to have to crop every photo you take with it?

If this had been a cheap zoom lens, I'd have expected the problem and not been bothered by it. With a fixed lens, however, I think there isn't much excuse.

Canon still charges about the same ($400) that I paid for this lens years ago. By now, they ought to have upgraded this thing, or dropped the price. It is the worst EF lens I own.

I was a bit concerned at first with the fixed focal length, but it has proven to be very versatile. It takes very sharp pictures, even when fully opened in low light. I have not noticed any of the vignetting that other users have mentioned.

Bottom line: great wide angle lens for the price. Useful for landscapes and tight space, low light situations.

Always happy with Canon Lenses.. I am more a detailed photographer, I purchased this mainly for my husband. He enjoys taking more landscape photography. Overall, very happy!