Canon EF 24-70mm f/2.8 USM L II - Full Format Review / Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

The distortion characteristic is above average for a lens in this class although it still produces a medium to high amount of barrel distortion at 24mm (~2.8%). This eases towards the middle of the zoom range. At 40mm images are basically distortion-free whereas there is a pincushion type of distortion again at 70mm (~1.3%).

Move the mouse cursor over the focal length text marks below to observe the respective distortion
24mm 40mm 70mm

Vignetting

The vignetting is comparatively low within the full format scope. There's still a heavy amount of light fall-off at 24mm @ f/2.8 (1.8EV) which will be readily visible in field images. The issue is better controlled at 40mm and 70mm although it's still far from being insignificant at f/2.8. Stopping down to f/4 resolves most of the issue at 40mm/70mm and at f/5.6 it's also no longer really relevant at 24mm anymore.

MTF (resolution)

The resolution characteristic of the Canon EF 24-70mm f/2.8 USM L II is pretty good but not outstanding. However, there's is one really good news here - unlike its predecessor the field curvature (flatness of the focus field) has been substantially improved.

At 24mm, the lens reaches its highest performance. The center quality is pretty much outstanding here straight from f/2.8 and all the way up to f/8. The border region is now on a very good level and at f/5.6 it's even in excellent territory. The extreme corners are pretty good at max. aperture already and also make it to very good at medium apertures. This characteristic remains mostly intact at 40mm. At 70mm there's a rather pronounced drop in quality. This does not apply to the image center which remains excellent till f/8. However, the borders/corners are softer here reaching only good results at f/2.8 and f/4. Stopping down to f/8 lifts the quality up to very good results.

Please note that diffraction effects reduce the quality from f/11 onward at all focal lengths - this is simply a physical limitation.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Lateral chromatic aberrations (color shadows at hard contrast transitions) are well controlled. They peak at 1.2px at 24mm @ f/2.8 but even so this is very moderate. The issue is even less pronounced at 40mm and 70mm. Stopping down reduces the CAs a bit.

Bokeh

The EF 24-70mm II is a comparatively "fast" lens thanks to its max. aperture of f/2.8. It's surely not as capable as tele prime lenses but you can achieve a quite shallow depth-of-field specifically at 70mm so let's have a look at the bokeh (out-of-focus) quality now.

Out-of-focus highlights show a near-circular shape at large aperture settings but the inner zone of these "discs" is quite busy/nervous with an "onion-like" substructure. The circular shape remains mostly intact till about f/5.6.

As usual the highlight discs deteriorate a bit in the border region. However, the Canon lens does a vastly better job than most here because only the extreme corners are affected. This is probably a positive effect of the large-diameter front element.

The background blur is quite smooth resulting in a pleasing bokeh in many "mainstream" scenes. However, the foreground blur isn't quite as harmonious.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

Bokeh fringing at large apertures is a problem which is often not well corrected in fast lenses. However, the Canon lens is a positive surprise in this respect. There's only very marginal color fringing at max. aperture and these traces are basically gone from f/4 onward.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/2.8 f/4 f/5.6

These sample portions were taken at ~70mm.




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