Canon EF 70-300mm f/4-5.6 USM IS II - Review / Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

The Canon EF 70-300mm f/4-5.6 USM IS II produces a fairly high amount of image distortions for a tele lens. At 70mm you will have to live with a medium barrel distortion (2.1%) switching to medium pincushion distortion at 200mm to 300mm. This is nothing extreme but it's visible in scenes with straight lines (i.e. architecture).

Vignetting

The vignetting characteristic is typical for a lens in this class. At fully open aperture, the light falloff varies around the 1.2EV mark. Stopping down by 1 f-stops reduces the issue to an almost negligbiel degree.

MTF (resolution) at 50 megapixels

Given the fact that the Canon EF 70-300mm f/4-5.6 USM IS II is a consumer lens, the resolution figures are pretty good. The quality is very good in the wider center zone at 70mm. The border quality is still good at f/4 here and it improves to very good levels at medium apertures. The extreme corners are quite soft though. The sweet spot is in the middle range. The center quality may be a tad reduced here but the results are on an evenly high level across the image field. At 300mm the sharpness is generally a bit lower again but the lens still manages to achieve a good to very good quality.

The centering quality of the tested sample was Ok with some variations at 300mm. The field curvature is somewhat higher than average.

Please note that the MTF results are not directly comparable across the different systems!

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

MTF (resolution) at 21 megapixels

Why are the MTFs sometimes "better" on 21 megapixels compared to 50 megapixels ? There are two reasons for this. Lateral CAs are lower in terms of pixel widths at 21mp simply because the pixel density is also lower. Extreme CAs that may exist at 50mp are less affecting the measurements at 21mp. Generally, we are also using a certain degree of sharpening during the image conversion (just like in real life images) and because the 21mp results are "sharper" on pixel level they are relatively more receptive to (mild base-) sharpening.

The majority of users are still using cameras with a more moderate pixel count so let's have a look how the lens performs with the eased requirements at 21 megapixels - also in order to be able to compare the results to older reviews.

Unsurprisingly the results are seemingly "better" (sharper on pixel level) across the board. The center quality is great at 70mm at f/4 to f/5.6. The borders are very good whereas the corners still show some softness at f/4, albeit the situation improves when stopping down. Unsurprisingly the sweet spot remains around the 200mm mark with a very good to excellent center quaity and a very good outer image region. The resolution is slightly reduced at 300mm but still on a very good level.

Please note that the MTF results are not directly comparable across the different systems!

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 the image borders) are very low. At 70mm they vary around the 1.2px mark at the image borders. The 200mm setting shows the lowest, average CA pixel width of just 0.3-0.5px. The CAs increase again at 300mm but they remain very low levels.

PS: The CA figures were taken at 50 megapixels.

Bokeh

Due to its max aperture of f/4-5.6, the Canon lens is hardly a bokeh monster but you can easily produce shallow depth-of-field images when shooting at short to medium focus distances. We didn't do our full analysis this time but let's at least have a look at the characteristic of out-of-focus highlights.

Thanks to the 9 aperture blades the (near-center) highlights are nicely circular at f/5.6 and even at f/11. However, they show a bit of outlining as well as an onion-like sub-structure which is emphasized the more you stop down. The circular highlights deteriorate to the usual "cat eyes" the more you move to the image corners. As usual stopping down helps with this albeit from a real-life perspective you won't really do so due to the small max aperture anyway.