Canon 100-400mm II only reaches to 370mm?

Started Jun 20, 2019 | Discussions thread
Steve Balcombe Forum Pro • Posts: 14,713
Re: Canon 100-400mm II only reaches to 370mm?
1

Lemming51 wrote:

  • The reviewer's test was at the min. focus distance for the 400/5.6L (3.5m)

Yes, and this is really important - he's chosen the optimum setting for the 400, effectively setting the others up to fail. But the 400 fails pretty spectacularly at 2m.

Spoiler - all 3 have effective focal length much shorter than the nominal 400mm when focused closer than infinity. In fact, the 400/5.6 focused to 3.5m gives max. magnification of 0.11x. Using "thin lens" formula approximation, this is an effective focal length of just 312mm. The 100-400 apparently is a bit shorter than that at 3.5m. The 100-400 focuses much closer to just 0.98m where it achieves much greater maximum magnification of 0.31x, but that's equivalent to about 177mm.

The 100-400L II has the worst focus breathing of any lens I've ever used, but actually in use it's not much of an issue. Getting 0.31x magnification from a metre away is superb for butterflies, dragonflies, other large insects, reptiles and amphibians, and more. Three times better than the 400 prime, FWIW. And if that's still not enough, the images are dead sharp (helped by the four-stop IS) so they'll take a good deal of cropping for a tighter composition. If you didn't know the calculated focal length you wouldn't even know you had a 'problem'.

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