Canon EF-S 17-55 mm f/2.8 IS USM
7. Coma and astigmatism
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The coma is well corrected. It can be seen on the same level for every focal length and only for a wide-open aperture. After stopping down the lens to f/4.0 the problem basically disappears.
The second commonly present abaxial failure - astigmatism - is very well corrected. The average difference between the horizontal and vertical MTF50 values measured in the center was only 4.6%.
