Canon EF-S 18-135 mm f/3.5-5.6 IS STM review - Coma, astigmatism and bokeh

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Canon EF-S 18-135 mm f/3.5-5.6 IS STM

21 September 2015

Arkadiusz Olech

7. Coma, astigmatism and bokeh

Thumbnails below show clearly that the tested lens doesn’t have any noticeable problems with coma correction. That aberration is perhaps not controlled in a perfect way but still it is not a good reason for serious complaints either.

50D, 18 mm, f/3.5, center	50D, 18 mm, f/3.5, corner

50D, 35 mm, f/4.5, center	50D, 35 mm, f/4.5, corner

50D, 70 mm, f/2.8, center	50D, 70 mm, f/2.8, corner

50D, 135 mm, f/5.6, center	50D, 135 mm, f/5.6, corner

The astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 5.3%. It is hardly a negligible value but still can be considered low. It’s worth mentioning the fact that the aberration reaches its peak at the 18 mm focal range where it amounts to 8%.

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When it comes to the appearance of defocused areas the situation is surprisingly good. It is true that you can notice a lighter rim and truncations in the corners which stem from the vignetting but you have to remember you deal here with a cheap megazoom so you should be more forgiving.

50D, 122 mm, f/5.6, center	50D, 122 mm, f/5.6, corner

50D, 122 mm, f/5.6, center	50D, 122 mm, f/5.6, corner

50D, 122 mm, f/8.0, center	50D, 122 mm, f/8.0, corner