I am looking at getting an 85 1.2L and need to replace the little 85 1.8.
I am hoping to get the 28-105 II as it seems to get rave reviews.
The need for this is simple. The 85 1.2 will be too heavy for mountaineering / expedition work and the 85 1.8 will collect dust if I am not on that mission. I am hoping to get *Really* sharp images from the 28-105 in the range of 35-85 at F 8.0. The sharpness at infinty must be at least decent. The enormous 24-70 2.8L is out of the question. The Tamron 24-70 2.8 is supposed to be good but is too heavy for this slot in my line up.
The KEY thing here is that this is strictly full frame, cropped sensors are not a practical comparison.
I have both the 85 1.8 and 28-105 II. There is absolutely no question that the 85 is the sharper lens at equivalent apertures, but for a variable aperture mid-sumer lens, it is quite sharp, and should more than fit the bill at f8. I have not used the 28-105 on a full frame digital sensor, but it performed fine on my film body. The corners may be a concern on digital full frame, but I will say this - I think my 28-105 actually performs better on my 20D than it did on my 7n (in terms of focus accuracy and overall apparent sharpness). It's sweet range seems to be in the middle of it's overal zoom range - it's maybe a little soft at 28, but from 35 to 105 (at least on my copy), it is consistently sharp. My lens has actually surprised me with it's sharpness wide open as well. Definitely not L-glass sharp, but for the money it's a definite keeper.
Again, my only concern would be corner performance on a full frame sensor, but from my experience with film and on my crop, it should be an outstanding performer for the price.
