Canon EF 24-70mm f/4L USM Lens Review

Canon EF 24-70mm f/4L USM Performance

At 24mm, sharpness in the centre of the frame is already outstanding at f/4, but the quality towards the edges of the frame falls behind somewhat, just falling short of good levels. Stopping down the aperture improves sharpness towards the edges of the frame with excellent clarity across the frame being achieved between f/8 and f/11.

At 50mm, the same pattern emerges, with very high sharpness in the centre of the frame at maximum aperture, accompanied by lacklustre performance towards the edges of the frame. Very good sharpness is achieved across the frame between f/8 and f/11 for this focal length.

Zooming to 70mm results in better performance across the frame on the whole, even at maximum aperture. Peak clarity across the frame is achieved at f/8 for this focal legth where sharpness is excellent in the centre and outstanding towards the edges of the frame.

Resolution at @24mm		Resolution at @50mm
Resolution at @70mm		How to read our charts The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column. The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple. For this review, the lens was tested on a Canon EOS 6D using Imatest.

Chromatic aberrations are reasonably well controlled, just exceeding three quarters of a pixel width at f/4 at either extreme of the zoom range. This low level should cause very few issues, even in large prints and harsh crops from the edges of the frame.

Chromatic aberration at 24mm		Chromatic aberration at 50mm
Chromatic aberration at 70mm		How to read our charts Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software. Apochromatic lenses have special lens elements aspheric, extra-low dispersion etc. to minimize the problem, hence they usually cost more. For this review, the lens was tested on a Canon EOS 6D using Imatest.

Falloff of illumination towards the corners of the frame is quite pronounced for a lens with a maximum aperture of f/4. Here the corners of the frame are 2.04 stops darker than the image centre and illumination isn't visually uniform until the lens is stopped down to f/8. Falloff is slightly less pronounced at 70mm. Here the corners are 1.82 stops darker at f/4 and illumination is visually uniform by f/6.3.

Distortion is pretty well controlled for a lens of this type. At 24mm 2.07% barrel distortion is present, which is replaced by 0.704% pincushion distortion at 70mm. The distortion pattern is uniform across the frame, which should make applying corrections in image editing software afterwards relatively straightforward.

Even without the supplied petal shaped lens hood, resistance to flare is high and contrast remains excellent, even when shooting into the light.

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