Summary: I chose this lens because I needed a good medium telephoto. When searching the web for one I wasn't happy with how much overlap to the focal lengths I already have and thought purchasing some varible zoom, like the 24-105 for example, would be a waste of money since I already have a very good 17-50mm f2.8. I did some simple test shots both indoors, indoors with flash, outdoors in sun, and outdoors in shade.
Summary: Thank you for your service. I was looking for this lens. It looks that the description "new" wasn't very accurate - the lens works perfect only in auto-focusing mode. In manual mode it has sometimes problems. So I could probably rate it only as "average".
Summary: The pros and cons of this lens have been thoroughly debated already, but one significant weakness that I wasn't expecting was purple fringing on the boarders of high contrast areas. I planned on using this for wedding photography, but at f 2.2 and below I would get thick purple fringing around candles (or pretty much any light), around the brides dress, and basically any other high contrast transition.
Summary: I have used this lens only a few times but I have noticed that the quality of shots varies between shots under the same conditions. Often the photos are not focused, even when I use the auto focused. However, when they are in focus, the quality is great. The size is great, not too bad, fits in my camera bag with room for another lens.
Summary: POSITIVES: This lens is crisp at any aperture. At f/1.8 the bokeh is very smooth and predictable. The focal length (equivalent to 136mm on my 400D) is perfect for photographing a medium size choir from the back of our church, and is great for taking pictures during concerts without standing between the performers and the irritable people who sit in the front row.
Summary: I am a wedding photographer and I use this lens for head and shoulder portraits. This lens is not the sharpest lens I have used and this is disappointing considering it's a prime. It’s ok if you don’t make large enlargements; however I have used zooms that out perform this lens in sharpness. Of course the f/1.8 produces great DOF.
Pros: Consistent Output, Durable, Easily Interchangeable, Easy To Clean, Lightweight, Rugged, Strong Construction
Summary: This is a great and fast portrait lens. I wasn't sure if I would need it, as I already have the 24-105 f4L IS USM and 70-200 f4L IS USM, but after reading the reviews and reasonable price I thought it would be worth the shot. I found this lens generally produces my best portrait shots, and is fast under lower light conditions. Most of my portraits are under window light, so even f4 sometimes is too slow at 1/20 of a second or more.