The group of potential candidates is pretty small. There is the Canon 50mm 1.8, the Canon 50mm 1.4, the Canon 50mm 1.2L and last but not least the Sigma 50mm 1.4. It was easy to throw two of them out of the race very early. The Canon 50mm 1.8 is too cheap and the Canon 50mm 1.2L is too expensive. So it was up to the two 1.4 lenses to make the race.
If you read reviews and stuff out there you'll come to the conclusion that the Canon 50mmm 1.4 is a very good choice. Cheap enough, fast, sharp and reliable. Reviews of the Sigma 50mm 1.4 nearly always praise the optical quality and prefer it over the Canon lens. But it costs a bit more. The rating of the Sigmas auto focus is mentioned a lot of times to be not the best. But there are other opinions out there too.
Since it's very easy to order and return items today I simply ordered them both. Please finish reading this article to avoid missing the result ;-)
Canon 50mm 1.4
This lens was released in 1993 and it feels like this. I must admit that I'm spoiled by the quality of my L lenses. The Canon 50mm 1.4 lens feels not very sturdy and the USM motor is not very quiet. The lens extends while focusing and I think you should avoid any knocks against the extended barrel. In general it feels like a toy lens especially because of its low weight of only 290g/0.64lb. But once attached to a camera it's capable of capturing sharp images. The auto focus speed is good as well. Especially if you want to minimize the weight of you gear for a trip this lens is a good choice. Typically for a non L lens the Canon 50mm 1.4 ships without any accessories except the two lens caps. You need to buy a lens hood yourself.
Sigma 50mm 1.4
What a hunk. This lens weights 505g/1.11lb and feels exactly like this. The build quality is very good. It feels as nothing can harm it. And actually my son unintentionally gave the tripod a little push during I tested the auto focus accuracy. The tripod fell over and the lens crashed directly on the wooden floor. It got a very small bulge but continued working fine. So the feeling about the build quality was right. I guess the same accident would destroy the canon lens. When it comes to the optical quality of the Sigma lens then I can't complain. It's very sharp, it has a very beautiful bokeh. Accessory wise everything you need is included. There are the two lens caps, a carrying case and the tulip shaped lens hood.
Canon vs. Sigma
So having both lenses in front of me it was time to decide which one it should be. The better auto focus performance of the Canon or the better bokeh and build quality of the Sigma? After doing some focus tests with both lenses I opted for the Canon. The Sigmas auto focus was just unusable even with applied auto focus micro adjustment setting in the camera. This was the case especially if used in artificial light conditions. Most of the time the Sigma was simply out of focus or better out of focus of the region I expected to be sharp. So I was very disappointed and I send back the Sigma lens. But the story is not over.
After having the Canon in use for two weeks I felt like giving the Sigma a second try. I didn't like this toy feeling of the Canon lens. In addition I encountered auto focus issues with this lens too. So I ordered two additional Sigma lenses and did some auto focus tests. The following images shows the result. I know, this is not a very professional testing setup but it worked for me. The images show one image from the Canon 50mm and two image shoot with the Sigma lenses. You can tell the Sigma lenses apart by the last three digits of their serial number: 134 and 170. For the chart test I quickly printed out this chart. The camera pointed in an angle of approximately 45 degree to the chart.
Camera in parallel to the box, larger distance at f2.8, tested in addition with the Canon 24-70 2.8L
Camera in parallel to the box, shorter distance at f1.4
Camera in parallel to the box, bigger distance at f1.4
Turn 1 with a focus test chart, f1.4
Turn 2 with a focus test chart, f1.4
Turn 3 with a focus test chart, f1.4
The results gave me the direction for preferring the Sigma even more. The auto focus was not too bad this time and as you can see even the Canon lens made some mistakes. If you come to a different conclusion please don't tell me. I'm now very confident of my Sigma lens and I don't want to rethink this ;-)
Real world images
This is basically the most important section. All the tests do not matter if the lens performs well outside the test track. And basically both do. The Sigma provides a smoother bokeh which I like. You can clearly see kind of visible dots in the background of the first three images while the background of the other three images shoot with the Sigma lens are more smooth.
