I have given my brand new EF 70-300mm II IS USM a thorough pacing. Short story, I am happy with the purchase. Balancing the IQ, usability, and price, this lens is worth the cost. Read on for the long story.
Backstory: I am moving to smaller, lighter gear. Ostensibly, the 80D/70-300 II will replace my 1D4/100-400Lc for sports and athletics works. I have not quite decided yet, but so far, the new setup is performing well.
Notes: I compared this lens to the 70-200 f/4L IS USM at 70mm, 100mm, 200mm. I compared this lens to the 100-400Lc at 100mm, 200mm, 300mm. I did NOT use hoods on any of the lenses because I don't have one for the 70-300 II, yet.
This is my second nano-USM lens. I remain astounded by the speed and accuracy of this new focus system. It is lightning quick, and dead accurate. On top of that, it is silent. I can't hear it focusing in a dead silent house, with the windows closed. Casually, I'd rate the speed as about equal to the 85 1.8, or 70-200 f/4L IS. The AF on this lens is more than up to the challenge of shooting sports (if the aperture works for you).
The IS on this lens is, as expected, superior to the 100-400Lc. It is as good as the IS on the 70-200 f/4L IS. Again, it is dead silent. I didn't notice the difference when shooting the 100-400, it is pretty quiet. My 70-200 is the loudest IS of any Canon lens I've ever owned. The difference between the IS noise of the 70-300 and the 70-200 will make you think there is something wrong with your 70-200.
Let me start by confessing two assumptions. Number one, I half expected this lens to be on par with the other two. My experience with the 18-135 USM led me down that path; it is the best EF-s lens I've ever owned. The other half of me expected not quite so much from a $400 lens compared to $1100, and $1700 lenses. I got pretty much what I expected - somewhere in the middle.
I shot everything at ISO 800, 1/250, and f/5.6 on all lenses. Body was the 80D, BTW. To start with, both the L-lenses showed more contrast and more saturation than the 70-300 II. The 70-300 II also seems about 1/3 to 1/4 stop brighter (shot JPG) than the other two. For the sake of argument, I will assume the NOT insignificant differences in brightness, contrast, and saturation can be equalized in any PP software. I use LR6.
Sharpness was extremely good, considering the price of the lens. The AF speed and accuracy, along with way better IS, should put this lens on par with the 100-400Lc.
@ 70mm the L is slightly (pixel peeping) sharper
@ 100mm the L is noticeably sharper, no need to go to 100%
@ 200mm the L is slightly sharper
Remember, at 200mm, I am comparing a $400 lens shot wide open, in the middle of its range, to an $1100 lens, stopped down, at its maximum focal length.
The 70-300 II accounted well for itself against the 70-200L.
@ 100mm it is hard to see any difference
@ 200mm the L is slightly sharper
@ 300mm the L is sharper, but not by enough to make me hate the 70-300
The 70-300II looks as good at 300mm as the 100-400Lc does at 400mm
All in all, I am happy with this purchase. It crossed my mind to replace both of the L's with the 70-300 II. I am no longer in a hurry to do that. For one thing, the 70-200 on full frame (6D) is a smaller, lighter, faster, sharper, just plain better lens. If I keep the 6D, I'll keep the 70-200. The 100-400 is a different story. I really don't see the extra 100mm as a reason to keep it. The IQ is only marginally better than the 70-300, and the IS sucks on the 100-400. The downside to selling the 100-400 is current pricing. $700? Really? I know, I know, I have to consider the competition. Sigma, Tamron, and Canon all have equivalent focal length, arguably better lenses. Even my new 70-300 gives the 100-400 a run for its money. Maybe I'll relent after it sits in the closet for a year, unused.