Canon EF-S 17-85 mm f/4-5.6 IS USM
4. Image resolution
If we remember the results of the Canon EF-S 18-55 mm in this category, we notice that the new EF-S 17-85 doesn’t offer us anything better in the 17-30 focal length range. The cheap 18-55 didn’t do well at 55 mm focal length. This behavior is very typical for most verifocal lenses when the lens performs very well in one section of the focal length range to have a huge crisis in another range. A good zoom is one that maintains good results throughout the whole focal length range and the EF-S 17-85 mm demonstrates this kind of behavior. The MTF50 values are very similar at every focal length. An interesting fact: the lens’s best results were noticed at the 85 mm focal length and at open aperture. This is important since the lens doesn’t have the best aperture so the f/5.6 diaphragm will be frequently used.
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The situation is significantly worse at the edge of the frame. It is most visible at a wide view field of 17 mm focal length, where, as we learn later, the chromatic aberration and other perfectly co-working off axis defects impair the picture resolution. Therefore the Canon’s 17 mm results are much worse than, for instance, a kit lens’s 18 mm results.
The even picture resolution results kept at the whole focal length range are presented below on the testing board fragments taken at f/5.6 diaphragm and 17 and 85 mm focal lengths. In both cases, in slightly sharpened JPG format, the MTF50 values easily exceed the 1700LW/PH level and at the 85 mm focal length the values exceed 1880LW/PH.
