Top critical review
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Pick Your Subject Carefully!
on 25 May 2012
Context: I use this lens exclusively with an EOS7D. It was my last lens purchase, the rest of the family being 16-35mm f2.8L, 24-70 f2.8L, 70-200mm f2.8L.
Build quality, design and most of the ergonomics (operations) with this lens are superb, and just what you would expect from Canon L-Series Glass. One weak spot is the switch to flip Auto-Focus on/off, which can be fiddly to engage without removing camera from eye and looking at the lens barrel. You'll get it with practice, but slightly larger switches with a way to differentiate them at a tactile level would make a big difference...
In terms of size, weight and basic operation, it is similar in many respects to the 70-200mm f2.8, except for the trombone zoom. In practice this is not an issue, and the latter feature quickly becomes a pleasure to use. There are no surprises here [save maybe pleasant ones] for anyone familiar with other Canon lenses.
Everything gets interesting when we get to image quality, where IMHO my views differ from other posters. My experiences [after several thousand exposures with both this and the 70-200] are that they are very different lenses for very different purposes. This lens is great for creative portraiture; for shooting flora and fauna in ways that lets you bring in the subject. It can be good for close-up architecture and structural photography, where you want to focus on shapes, textures or details and move away from big canvas or traditional landscape shots.
However, it's weakness appears to be anything moving... There are several reasons for this:
1. The auto-focus is seriously slow in comparison with any USM lens. Unless you're shooting snails, don't be surprised if your subject can out-pace the auto-focus...
2. The 77mm [dia] primary lens - which works fine at 70-200mm - just isn't enough on a 100-400mm lens. It simply doesn't let enough light in. Can we have 82mm minimum please?
3. The aperture diaphragm operation is subjectively a *lot* slower than the 70-200mm f2.8L, so tracking a fast-moving subject across a light/dark background is an exercise in random chance...
The fact that you get f4.5-f5.6 says it all... it's just not quite fast enough, optically, to compete with the 70-200mm smaller sibling.
Using this lens with wildlife photography - particularly raptors [owls, hawks, buzzards, etc and at falconry demonstrations] I find that it just can't provide clear, crisp images in the way that the 70-200 does - to the extent that with hindsight I would probably have been better off with the 70-200 and the x2 converter. The slower optics - smaller aperture - means that you'll get longer exposure times that may result in motion blur.
So, scores well for pulling in static images at a distance, but not for anything involving moving targets, you're better off with the 70-200mm f2.8L and Photoshop's crop tool, or, if you can afford it, one of the longer Canon L Series Prime lenses... One caveat I'll offer to the above review... by current standards the 7Ds auto-focus system is very primitive, with a small number of auto-focus points to work with. It's possible that if you have a 5D Mk III or the 1DX, you'll get better results with moving subjects.
Summary: very good at what it does well, but sadly more of a niche lens that you would expect from a 100-400mm telephoto...
Update: (March 2013) A recent posting at the 'Canon Rumors' web site contained a story about the relationship between the batteries that Canon cameras use, and the speed and accuracy of lens auto-focus. To put it in a simple statement: Canon lenses work best with cameras equipped with big, hefty batteries - in other words their full-frame DSLRs. I thought this might be a useful edition to my review, and wanted to suggest that any potential buyer out there who owns a full frame Canon (5D, 6D, 1D, 1DS or 1DX) may expect to get substantially different results from use of this lens than I have experienced with my EOS 7D. In my original review I commented on the relatively sluggish performance of this lens compared with the 70-200 f2.8L - now I think I understand why this is the case. Hope this addenda helps.