8 out of 10 points and recommendedbuild quality, stabilization, versatility, colors contrast, decent sharpness(somewhat) slow focusing, awkward manual focus ring
This lens is used on a 7D.reviewed November 18th, 2015 (purchased for $1,067)
I moved from the 70-300L to this lens for extra reach. That is a great lens and if the focal length works for you, I'd actually recommend it over the 100-400, even though I think that it is overpriced and that it definitely should come with a tripod collar and nicer case for the price.
I have also owned the 400 f/5.6 before, but sold it when I bought my kayak since I wanted to shoot from the 'yak and figured IS would be a big advantage for that use.
As far as the 100-400 goes, it is a real work horse lens. I bought an older copy (UT) and was concerned at first that the rumors about copy variation would mean that I would have a soft lens. Luckily this turned out to be a false rumor (at least in my case). I did have to MA my lens to +7 though for optimum results.
The lens is sharp enough for my uses wide open, but does show some improvement stopped down. I like the fact that the MFD is much closer than the 400 prime since it makes the lens more versatile for closeups. Image stabilization is not as good as on the newer design, so I usually count on 2 stops compensation. I also wait for a couple of seconds for the IS to kick in, which seems to help. Colors and contrast are great. I have found the bokeh to be harsh sometimes in very busy backgrounds. The prime seems to be a little bit better in this area. The push/pull design makes the lens easy to transport but takes some getting used to. I usually either leave the tension ring all the way loose or cinch it down when I know I'll be shooting at 400mm. The manual focus ring is in an odd location next to the tension ring which I don't care for. Luckily I rarely use manual, so it's not a big deal. The autofocus is on the slow side for USM, but is usually fast enough. When shooting distant objects the focus limiter comes in handy.
My ratings on a scale of 1-10
Build Quality -9 Bokeh- 8
Focusing - 8 sharpness- 8.5
If you are expecting 70-200 II sharpness wide open then you will be disappointed. If you expect great results in a versatile package at a reasonable price, then you'll be very happy with this lens.
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