At 300 mm the image is useful even from the maximum relative aperture and on stopping down it reaches the borderline between good and very good level.
We already know there will be no record-breaking results.
As far as the image quality is concerned, the Sigma losesthe Canon at 400 mm is not only faster but also fully useful up to the maximum aperture.
Resolution graphs, presented in our tests, are so to speak the result of two factors the influence of optical aberrations and diffraction.
The graph below presents the results for the frame centre at focal lengths of 50, 135, 300, 400 and 500 mm.No wonders here but, after all, nobody expected them anyway.With the Sigma we get a wider range and a bit better stabilization but this device is a little bit more expensive.The Sigma 50-500 mm OS at 400 mm fares better than the 120-400 mm OS model and additionally we get a useful 500 mm at our disposal.The Sigma is no exception to this rule.It is difficult, though, because those lenses were tested on an EOS 20D so a camera with a significantly less densely packed sensor.As the tests of our lenses are based on unsharpened RAW files such a comparison is still possible.
Whats important and interesting at the same time, when you go from 400 mm to 500 mm you cant notice any change in the image quality.
Firstly the image quality increases because we limit aberrations by stopping down the lens, then it decreases because aberrations are minimized but the narrowed aperture makes the resolution drop due to diffraction.
In fact we knew about that trend from the very beginning because of laws of physics and the tested lenss parameters.The Sigma, however, boasts 50 mm and 500 mm focal lengths for a change which the Canon lacks.If we tested the 100-400L on the 50D we think for the combination of f/8.0 and 400 mm it would exceed easily the level of 40 lpmm.Body fat range chart for easy health assasment 6 memories, clear digital readout, maximum weight: 352Lbs, low battery indication.The value deemed by us as the decency level, black & decker alligator manual so 30 lpmm in the case of the 20D and about 34 lpmm in the case of the 50D, and the maximum results reached by the best primes which, on the 20D, are near 44 lpmm.When you compare the tested lens to the Sigma 120-400 mm OS we see a very similar situation.