Canon EF-S 18-135 mm f/3.5-5.6 IS
7. Coma and astigmatism
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The coma correction is surprisingly a strong point of the tested lens. At the longer end of the focal lengths range there are practically no problems with this aberration whatsoever. At 18 mm the influence of the coma on the shape of the diode is noticeable but certainly not medium, let alone high.
When it comes to the astigmatism we also don’t have any serious reservations. The average difference between vertical and horizontal MTF50 function values amounted to 6.2% which is a low result. The Canon could be praised here especially as we deal with a low-end construction with a wide focal lengths range. Such systems often feature a lot of plastic elements which not always are able to keep a lot of movable optical elements exactly on the axis. That’s why in the case of such lenses the astigmatism often reaches high values. Fortunately, the Canon managed to avoid these problems but we don’t know whether or not it will keep equally good level after a year or even several years of usage. We count on our Readers, who can share their opinions and marks in our lenses’ database – we shall be most grateful for Your feedback on the matter.
