I just purchased one of these, and went into it with the same reservations you have. After reading about the focus shift issues, and lack of sharpness, I was prepared for the worst. Like any lens, there must be sample variation, and some people luck out and get a lens that works well with their camera body straight out of the gate.
lancebroad wrote in post #14869241
The DOF focal plane is so razor thin at f1.2 a slight movement after focus results in stuff out of focus.
thestone11 wrote in post #14869290
+1 the dof is super thin at wide open for the 50L. Using the center point for AF and recompose will almost guarantee miss the focus on the spot you want it to be.
I made sure to test the focus/recompose thing while trying out the lens, and posted below are examples of how sensitive the DOF is to recomposing. From center focus, I shifted the lens less than one full brick to the side. Both shots are wide open, SOOC, with no sharpening or other presets. The crops are 100% crops, again with nothing done to them.
Center focus (no recompose):
Frame recomposed after center focus:
100% crop of static shot:
100% crop of recomposed shot:
I was pretty blown away by the results, both in terms of how sensitive the thin DOF is, and how sharp the lens is wide open. Having owned all the other 50mm options, and several other fast primes, the only lens that was sharper wide open was the 100L macro, which I guess isn't really a fast prime in the same sense.
Having used the lens for a day of product photography, I'm so glad I went for it. Most of what folks say is true: CA can be pretty rough in high contrast areas until about 2.8 or so, and lots of vignetting wide open. I haven't experienced focus shift yet, but maybe I haven't shot the right combination of aperture and distance. I've had the same focus results when using center point and outer points, and of course the backgrounds this lens produces are just lovely.
I'll definitely be keeping this lens, and would endorse it fully. I must say that I would probably do the same even if the lens were softer wide open. I've seen the sample thread images and they're still great even when a bit squishy.