Canon EF-S 55-250 mm f/4-5.6 IS
4. Image resolution
Let's take a look how the tested lens work in the center of the frame mounted on a Canon 20D.
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On the one hand, the presented results at a maximum level of 37 lpmm, are far from the results recorded by the best lenses on the 20D, which can reach up to 43 lpmm. On the other hand, we have here an amateur type 5x zoom, so it is hard to expect miracles in this category, so the Canon's performance can be assessed quite positively.
Taking into account different crop factors (1.5x vs 1.6x) on APS-C/DX sensors I decided that comparing this lens to a Nikkor 55-200mm VR gives us the same score. Both lenses seem to work quite well, giving equal behavior. I am particularly pleased that the focal length of 250mm does not drastically lower quality, relative to the others, and is fully usable, even for maximal aperture in excess of the maximum level of 30 lpmm, which we think is good.
On the other hand, if we look at the results of the Canon 70-300 IS, we can only envy it, looking at its 40 lpmm level for 70-135mm focal length and the fact that in this case, the focal length of 300mm is better than the 250mm focal length for the EF-S 55-250mm.
Resolution at the edges of the frame is again very similar to the Nikkor 55-200 VR. For all focal lengths we see an equal behavior in both lenses, which we think is a decent result. For instance, comparing the EF 70-300 IS with the 55-250 IS, latter’s behavior in the edge of the frame looks better than in the center. Although for shorter focal lengths the 70-300 IS performance looks better, it shows a larger dispersion and additionally, the focal length of 300mm looks worse than 250mm in the 55-250 IS.
In this chapter, once again, we are convinced that too much plastic in the lens body and manufacturer savings do not result in high quality pictures. The diagrams presented above are average values from several test charts, measured from both sides of frame left and right. The problem is that each test chart separately returned significantly lower resolution of the image on the left than the right. This effect was particularly visible at 55-135 mm focal length and almost disappears at 250 mm.
Traditionally, at the end of this section we present our selected pieces of the test chart obtained in JPG.
