Studio Tests (APS-C)

The Canon EF 24-70mm f/2.8L II USM performs exceptionally well on APS-C in the studio, matching or surpassing any other lens in its class (although the differences aren't necessarily huge). Sharpness is hugely impressive even at maximum aperture, to the extent that there's barely any measured improvement on the EOS 7D on stopping down to F8. Distortion, CA and vignetting are all very low too.

Sharpness Sharpness is exceptional, and notable for both its evenness across the frame and consistency from end to end of the zoom range. Indeed the lens is performing so well on the EOS 7D at F2.8 that there's barely any room for improvement on stopping down, with little difference in MTF50 between F2.8 and F8. This is a remarkable performance by any standards.
Chromatic Aberration Lateral chromatic aberration is extremely low. At wideangle there's a little blue/yellow fringing, which changes to red/cyan at telephoto. But none of this is likely to be objectionable in most real-world shooting.
Vignetting Vignetting is negligible, as usual for a full frame lens used on APS-C.
Distortion Distortion is low, which again is typical for a full frame lens used on APS-C. There's moderate barrel distortion at wideangle, which could be visible in highly geometric compositions . This reduces in zooming in, before switching to slight pincushion distortion at the telephoto end. But in real-world shooting it's unlikely to be visible across the majority of the zoom range (35-70mm).

Macro Focus

Macro (APS-C) - 100x67mm coverage
Measured magnification: 0.20x
Distortion: Negligible

Minimum focus distance*: 36.0 cm
Working distance**: 17.3 cm
Focal length: 70mm (112mm equiv)
* Minimum focus is defined as the distance from the camera's sensor to the subject
** Working distance is measured from the front of the lens to the subject

The 24-70mm II's measured maximum magnification using manual focus is 0.2x, fractionally higher than specified but still pretty typical for its class. Note though that SLRs won't generally autofocus quite this close.

Image quality at minimum focus is very dependent upon aperture. With the lens stopped down to F5.6 central sharpness is very impressive, but in our flat-field test chart shot the corners are soft due to curvature of field. Stop down further and they sharpen up pretty well. There's just a hint of chromatic aberration in the corners, and minimal distortion.

At larger apertures, though, image quality is much less impressive. At F2.8 the black lines on our test chart are shrouded by green-coloured chromatic aberration (click here for the test chart shot), to the extent that the image actually looks out-of-focus when viewed as a whole. At F4 this effect is reduced, but still visibly present; at F5.6 it's cleared-up completely. This has knock-on implications for focusing, and means the 24-70mm II isn't a great lens for selective focus close-ups. We'll look at this in more detail later in the review.

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. Here we're looking at issues specific to APS-C users; for a fuller picture, be sure to read the next page too.

Chromatic Aberration

Chromatic aberration is generally very low on APS-C bodies, and while Canon's most recent model, the EOS 650D can correct it in JPEG processing, older cameras such as the EOS 7D and 60D can't. In normal shooting it's most pronounced at wideangle, and shows up as green/magenta fringing towards the corner of the frame. Raw shooters can correct it easily in post-processing if necessary, of course.

The example below shows what you can typically expect - it's visible, but not hugely objectionable even without any correction.

Canon EOS 650D, 24mm F8, camera JPEG (CA correction disabled) 100% crop, top left corner