Canon EF 11-24 mm f/4L USM
4. Image resolution
Now let’s check how the tested lens compares here – its results in the frame centre at 11, 17 and 24 mm focal lengths presents the graph shown below.
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The results at the longer end of the focal spectrum are more or less identical and brilliant at the same time. Already at the maximum relative aperture the image is very sharp, with MTFs reaching over 43 lpmm. On stopping down those values increase to near 45 lpmm so a level no good ‘prime’ would be ashamed of. Mind you, this lens is a zoom device with extreme parameters, something unique and very hard to construct.
The 11 mm focal length seems to fare a bit weaker but only if you compare it to brilliant results we saw in the 17-24 mm range. Even at the combination of 11 mm and f/4.0 the MTFs of the lens exceeded 42 lpmm so were excellent and the maximum results of 43 lpmm are simply beyond reproach.
Still let’s check whether our enthusiasm survives the test results on the edge of the APS-C sensor.
Once again the 11 mm focal length is the weakest and the longer end fares better, the focal lengths even differing between each other for a change. You might still enjoy the performance of the lens because even at the maximum relative aperture the MTFs exceed 33-34 lpmm so stayed safely above the decency level. Near the f/8.0 aperture the results can get as high as 40 lpmm – a value definitely worth noticing and praising when it comes to an ultra wide-angle lens.
There is one more hurdle left and it is also the most difficult one - the performance on the edge of full frame. Let’s have a glance at the graph below.
At the longer focal lengths there are no objections – even at the maximum relative aperture the image is fully useful and on stopping down the MTFs can exceed 35 lpmm. If you really want to find something to complain about then look at the combination of 11 mm and f/4.0 where the MTFs brush against 30 lpmm so are right below the decency level. That level is reached only near f/5.6 – 8.0. Still if you keep in mind the wide angle you deal with here those 1-2 lpmm short of the decency level can be forgiven and forgotten.
At the end of this chapter, traditionally we present crops taken from photos of our resolution testing chart, saved as JPEG files.
| Canon 5D MkIII, JPEG, 11 mm, f/4.0 |
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| Canon 5D MkIII, JPEG, 17 mm, f/5.6 |
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