I'm looking to invest in some L series prime lenses. I'm working towards owning both the 7d and the 5d Mk2 (or 3 soon). I've heard nothing but glowing reviews of the 35mm 1.4, the 50mm 1.2, and the 85mm 1.2. But besides the 35 being a bit faster is there much difference between these lenses? Would I simply be picking one based on how close I predict being from my subjects or do the lenses actually perform better/worse?
I'm new to photography, but from what i'm slowly learning - yes - they're great lenses, but they each have unique characteristics, primarily their focal length -
Jasmine Star covers these lenses and their effects here: http://www.jasminestarblog.com/index.cfm?postID=990&review-canon-mm
(and here gear guide covers those lenses here http://www.jasminestarblog.com/index.cfm?postID=1233&jasmine-star-lenses-and-camera
Even if you've got the subject the same position and size in the frame - they're going to look different - think in the extremes fish eye all the way up to compressed at the 300mm look. You've also got an effect on the compression of the background - the larger focal lengths will compress the background more, magnify it more and vice versa.
7D's a cropped sensor, so your lenses will look different between a 5D Mark II and the 7D. Effectively using the 35mm on the 7D, you'll see a cropped version of what you'd see on the 5D. Great lenses, and i'm sure many would love to get them too! As for characteristics, you've got AF, time till update, sweet spot for their aperture (is similar?).
Your proximity to the subjects is one issue, but as above - they're going to look different, even if you move your feet so the subject is the same size in your shot.
Looking to get all 3 might not help you improve so quickly as getting to know one, then building from there - e.g. choosing to do portraits, you could take the 50mm on the 7D (similar to 85mm due to the crop), then it'll be 50mm on the 5D.
What are your subjects? What do you want to shoot, and how? Do you like tight in close crops of people, or wider views?
(the the-digital-picture.com/Reviews/ of these lenses I think goes more into the usual uses of these different lenses).
Final point - it's going to take some getting used to focusing, and shooting with these wide open - the depth of subject that'll be in focus will be very thin. Double edged sword of the lenses!