Tuesday, 2 October 2007

Canon EF-S 17-55 f/2.8 IS: a footnote

In my part 2 of my 2 part review (part 1 here) I made the statement regarding tilt of the lens due to the zoom mechanism. I left the statement hanging somewhat and realised that I should do a check to see if the impact is as expected.

As a result, I've run tests on a series of targets with perpendicular features (wall & floor) to test for non-parallel focal plane.

Test run by taking shots at f/2.8, manual focused on the wall at the centre of the lens. I've then checked the relative focus of the paving slabs on the floor to see where the focal point lies. If the focal plane is parallel to the film plane, the wall should be in equal focus, if not, there will be a point on the slabs that is sharper.

Overall conclusion: at a variety of shorter ranges (less than hyperfocal distance), focus accuracy and possibly depth of field (combined with sensor resolution) swamp any tilt effect. I've also discovered my 17-55/2.8 has a slight tendency to front focus (but that's another matter entirely).

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