Canon EF-S 18-200 mm f/3.5-5.6 IS
4. Image resolution
On the one hand you can complain a bit here – after all at no combination of focal length and aperture the lens doesn’t even approach the value of 50 lpmm. The Sigma 18-250 mm OS, tested not so long ago also on the Canon 50D, didn’t have such a problem at shorter focal lengths and its focal range is even wider. On the other hand the Canon’s performance is very even. Near the maximum relative aperture at all focal lengths it reaches the level of 40 lpmm or higher. As a result it provides images of good or even very good quality after a slight stopping down. What’s important, the longest focal length doesn’t lag behind others and the lens performs very nicely here, giving fully sharp pictures at such apertures which are still not limited by diffraction.
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While in the frame centre we didn’t have to make a great effort to find some advantages of the tested lens, the edge of the APS-C sensor is far more problematic.
Here, for a change, at the maximum relative aperture and all focal lengths, the images are not very useful. What’s more, even after closing the aperture by about 1 EV we can’t be sure of full usefulness of images. The best situation is at 18 mm where, starting from f/4.5, we can talk about a decent quality of images. The worst performance is witnessed at 100 and 200 mm where only on stopping down to f/11 we can come near the area close to 34-35 lpmm. The crisis, observed at longer focal lengths, although serious, is still less acute than in the case of the Sigma 18-250 mm OS, which, at the maximum relative aperture, reached results on the level of only 20 lpmm.
The crops below were taken from the frame centre of our resolution chart photos. We used JPEG files here, which we saved along RAW files - the source of data presented on the graphs above.
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