Sigma S 70-200 mm f/2.8 DG OS HSM
4. Image resolution
Let's check how the results of the Sigma S 70-200 mm f/2.8 DG OS HSM compare here; below you see a graph with appropriate values from the frame centre at 70, 135, 200 and 280 mm (TC).
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In the most interesting aperture range so from f/2.8 to f/5.6 extreme focal lengths are actually the best. Already at the maximum relative aperture you get 43-44 lpmm and on stopping down to f/4.0 the resolution increases to 45-47 lpmm. These are really impressive values for a zoom lens.
At the maximum relative aperture you observe a slight decrease at 135 mm focal length but, fortunately, stopping down eliminates that problem very quickly and from f/4.0 the middle of the range is as good as the performance on both ends.
A performance with the 1.4x teleconverter attached to the Sigma is quite another matter. Compared to the resolution at 200 mm the decrease of the image quality is quite noticeable. Fortunately the 200 mm performance was sensational so the 280 mm focal length still might be called good – at the maximum relative aperture it brushes against 37 lpmm and on stopping down the aperture by 1 EV it approaches 40 lpmm.
An interesting phenomenon can be observed on significant stopping down. Theoretically, at that point the resolution is limited just by diffraction so all the results should be the same for all focal lengths, within the margin of error of course. Meanwhile the values reached with teleconverter even by f/16 and f/22 are noticeably below the level you can observe at 70-200 mm. Such a performance might suggest that after attaching the teleconverter the whole system stops down the aperture a bit more than declared or the multiple of the converter itself is a tad bigger than the official 1.4x.
Now let's check how the tested lens performs on the edge of the APS-C/DX sensor – an appropriate graph is shown below.
This time the 200 mm focal length seems to be the most sensible of all - in the range from f/2.8 to f/5.6 it keeps an even and excellent level of 42 lpmm. Roughly the same can be said about the performance of the 70 mm focal length - in that case only the maximum relative aperture lags behind with a result of less than 35 lpmm; by f/4.0 and f/5.6 you get the highest values of 43-44 lpmm. It is a level which, even several years ago, was reserved for just the best primes so the lens's performance is beyond reproach.
Resolution values you see at the 280 mm focal length after attaching the teleconverter once again lag behind the performance at the shorter end of the focal spectrum but, once again, it doesn't makes us worry. Even at the maximum relative aperture images remain fully useful and on slight stopping down resolution levels might be easily described as good.
Now let's check how the Sigma S 70-200 mm OS fares on a very demanding edge of full frame.
You can say only good things about the 70 mm focal length. Even at the maximum relative aperture you get at least good results and a value of 43 lpmm by f/5.6 should be called simply sensational.
Also in the crucial aperture range at 200 mm you see a very good resolution level, that of 36-37 lpmm.
Some reservations concern only 135 mm where the tested lens has to be stopped down to near f/4.0 in order to enjoy really useful images.
What's interessting, we have no reservations when it comes to the performance with the teleconverter. Even at the maximum relative aperture you get MTFs of 30 lpmm so a level guaranteeing you a decent image quality. Such values gain our recognition especially as you deal with a very demanding edge of full frame and the teleconverter has to cooperate with a zoom lens.
Thish chapter proves that Sigma is able to produce not only sensationally good Art series primes but also zoom lenses. A minor crisis observed at 135 mm and on the edge of full frame cannot change our very favourable opinion of this lens in any way.
It's also worth reminding here the resolution performance of the predecessor of this lens so the Sigma 70–200 mm f/2.8 EX DG APO OS HSM. Even then Sigma did a good job because the results in the frame centre of both these lenses are very similar with one difference – in the case of the older model the maximum focal length fared a bit weaker. The new instrument performs better on the edge of the frame, especially in the case of full frame; its predecessor fared weaker at the maximum relative aperture and at 70 mm which could be considered useful only from f/8.0 onwards. Also the performance of the older lens on the edge of the frame with the teleconverter attached left a lot to be desired.
At the end of this part of our test, traditionally we present crops taken from photos of our resolution testing chart which were saved in the JPEG format.
| Canon 5D MkIII, JPEG, 70 mm, f/4.0 |
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| Canon 5D MkIII, JPEG, 135 mm, f/2.8 |
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