First of all, Canon spoken here only. Second, Wikipedia has a really great article about 50mm lenses here.
My two cents: The 50 comes in four forms:
the great (1.8, $100)
the awesome (what I use, 1.4, $350)
the drool-inducing (1.2, $1500)
and the unicorn of lenses (1.0, out of production, very few made).
The 1.8 is perfect and definitely where I would start! You will get a lot of use out of it. The differences are lowest aperture available (thus the 1.x numbers) and the chromatic aberration (technical explanation here). Chromatic aberration is a weird blue or red ghosting around areas of highlight you can get when you shoot at the lowest aperture available. The 1.8 gets it badly, the 1.4 gets it a little, and apparently the 1.2 doesn’t get it at all. It’s only noticeable when viewing the digital image closely. 1.2 owners, feel free to weigh in on this subject.
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Note: I did forget to mention the 2.5 Macro. Now that I’ve remembered it, I’m going to purposely exclude it from the post. Ha! The lenses mentioned above are coveted for portability, speed, and performance in low light situations- all important when documenting events. The Macro 50 doesn’t compete in those areas. It’s built for detail and is relatively slow compared to the list above. A great addition to anyone’s bag, sure, but just not in this list.
