Canon EF 70-200 mm f/4L IS II USM
10. Autofocus
Still you cannot call the focusing mechanism quick. Running through the whole focusing distance and confirming the focus takes about 0.8-0.9 of a second. It seems that time is slightly shorter when the lens goes from infinity to the minimum focusing distance.
Employing the focus limiter and the range from 3 meters to infinity helps – then the focusing mechanism works with lighting speed and the focusing time is shortened to less than 0.3 of a second.
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It's a pity Canon didn't take a leaf out of independent producers' book and doesn't allow you to calibrate every aspect of the autofocus mechanism, setting the range of its work included.
We didn't have the slightest reservations concerning accuracy of the mechanism for a change. After the right microcalibration the lens always hit where it should without any mistakes.
In the case of the EOS 50D the autofocus of the tested lens had a back-focus tendency. That effect was visible at all focal lengths and it disappeared only after attaching the teleconverter. When we passed to the 5D Mark III back-focus became much less pronounced and really difficult to perceive in real life photos.
| Canon 50D, 135 mm, f/4.0 |
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| Canon 50D, 200 mm, f/4.0 |
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| Canon 50D, 280 mm (TC), f/5.6 |
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| Canon 5D Mk III, 135 mm, f/4.0 |
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| Canon 5D Mk III, 200 mm, f/4.0 |
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| Canon 5D Mk III, 280 mm (TC), f/5.6 |
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