Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. The Canon 100mm F2.8 L IS USM Macro gave consistently excellent results, through a combination of superb image quality, generally accurate autofocus and (at longer distances at least) effective image stabilization.


Like many lenses with a relatively narrow angle of view, the 100mm Macro isn't at all happy when bright light sources are directly in shot - then again there aren't that many pictures you'd want to take with it where this is the case (sunsets maybe). The results aren't pretty at any aperture, but as usual multicolored flare patterns become ever more pronounced the further you stop down.

Shoot with the sun just slightly out of the frame and although flare can persist, it's much less problematic. Overall though, given the complexity of the lens's construction and the exposed nature of the front element, we'd recommend (even more than usual) using the hood in bright light as a matter of course.

F16, Canon EOS 5D Mark II F11, Canon EOS 5D Mark II

Background blur ('bokeh')

One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. The 100mm F2.8 macro is capable of delivering substantial background blur, although portrait shooters should note that technically it simply can't match its short telephoto stablemates, the EF 85mm F1.2 L II USM and 135mm F2 L USM.

In general, bokeh is extremely pleasant; at macro distances it is, as we might expect, extremely smooth and 'creamy'. What tends to be more problematic for macro lenses, though, is bokeh in the 'portrait' range, focused to around 1 - 3 meters with the lens wide open. But even here the background is still attractively rendered, with no harsh, bright-ringed edges to the highlights. It's not quite the best you'll ever see, but it's very nice indeed.

Close-up Bokeh
Distant Bokeh
F2.8, Canon EOS 5D Mark II F2.8, Canon EOS 5D Mark II
50% crop 50% crop

Diffraction softening at small apertures

To demonstrate how the effect of diffraction depends upon the camera's sensor, we repeated our previous diffraction test but now using the EOS 5D Mark II as test body. We've kept the image size nearly the same, which means moving the camera closer to the subject. With the 5D Mark II's larger pixel pitch, visible blurring doesn't begin until about F11, and F16 still gives quite acceptable results. This is pretty much what we expect from theory.


Once again, the optimal aperture to use depends upon several factors - including the final print size and the desired depth of field. Clearly some detail which appears to be within the depth of field at F32 in the reduced size image is distinctly unsharp when examined at the pixel level.