Canon EF-S 55-250 mm f/4-5.6 IS
5. Chromatic aberration
Looking at the chart above we see that the chromatic aberration isn't a serious problem. Only at 250mm does it reach an average level, while at other focal lengths it is low.
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But it is still a picture resulting from averaging results from different test charts, which, in this case, doesn’t reflect all the details. Similarly to the image resolution results, only maximum focal length behaves evenly showing a similar aberration level on the left and on the right side of the frame. When using shorter focal lengths, we start encountering some problems. To see just how serious these problems can be, see the chart below, which shows the aberration for the55mm focal length being measured separately for the right and left side of the frame.
The chart is very interesting in that it shows us that the aberration for f/4.0 on the left side is minimal, while on the right side is maximal. The situation becomes completely opposite when we start stopping down the lens. It’s worth noticing that we notice a similar phenomenon at 135mm focal length, as can be observed on our test chart clippings.
The facts speak for themselves. The plastic body, plastic bayonet and plastic mechanism with its moving lenses are simply not ideal conditions for keeping the lenses in-axis. When the conditions aren’t perfect we notice such effects as the maximum resolution area moving respect to the center of the frame, as well as strange chromatic aberration results.
