Slight conundrum over here and not quite sure which way to go. I have a 7D and an 5dmk3. Since I bought the mk3 the poor 7d has sat on a shelf. I brought it with me on a few weddings but just could't reason why I'd bust it out (go figure, can the 7d pull down awseom f8 images at 1/125th and ISO 6400??? Nope...lol. On the last wedding though, I did find myself not liking the run back to my lenses to swap (missing the moment), or staying with the lens on camera (getting the moment but not in the way I wanted). I have a 24-70 and a 70-200 currently. So what I am thinking is pick up a fast prime for the 7D (or, save up for a second mk3!).
So, which primes would work? I really like the idea of a 50mm 1.4, but, i think I'd really like that for the mk3. 50 on a 7d would be more like 80mm. So would that lead to too much overlap? I want to be able to pull the 7d back into the fray. Would a 50mm be too long? Other lenses I'm considering, the 28 1.8, not as fast as the 50, but it would be like a 50 on FF. The 35mm 2.0 also looks nice, it's a stop less than the 28, but closer to the range I'm thinking. Or, more expensive but go the opposite direction - the 135mm 2.0 (hard to bite the bullet of a $1000 lens for a backup body).
I feel like the 50mm has the most use on both camera advantages (for when I want to go nutty with DOF). But 50 is more like 80 on the crop which makes the decision difficult. 80mm does not fit, lol. I'm either range limited or range duplicated (why use the 7d+50mm if i have the 70-200 mounted on the mk3, and, if i have the 24-70mm mounted on the mk3 the 50 on the 7D really isn't a bump in range.) Should I consider an 85mm 1.8? (go 85 on the 7D and 24-70 on the mk3???) uggg....not sure which way to go...
I used the Sigma 30mm 1.4 on my 50D when I started making money from this craft. on that crop the Siggy will stand up! I vouch for it so much that it was a no-brain er to get the Siggy 50 1.4 when I bought my 5D2. The Sig 50 was no where close to the IQ and color of the 30 so i sold that off. but trust me, the 30 on a crop is GREAT. test one in store and I'm sure you'll end any head aches about what to do.
besides, why not use a harness for both cams (in which I do- the black rapid brand) to stay prepared for any shots.