Lens review

Sigma 18-125 mm f/3.8-5.6 DC OS HSM

4 September 2009
Arkadiusz Olech

4. Image resolution

The image resolution of Sigma 18-125 mm OS, in terms of MTF50 values, has been measured on the strength of RAW files from Nikon D200. The measuring errors oscillated between 1.3-1.4 and 2 lpmm at maximum aperture and lowered when stopping down to 0.3-0.5 lpmm. The graph below shows the behavior of the tested lens at the center of the frame.

Sigma 18-125 mm f/3.8-5.6 DC OS HSM - Image resolution

At the first glance the results are good. Sigma’s problem is, the competitors are good too. Nikkor 18-105 mm VR performs the best, it has the results at the level of 40 lpmm or higher at practically all apertures. Nikkor 18-135 mm shows larger dispersion, but at its weakest focal length of 135 it’s still slightly better than Sigma at 125 mm. Sony 16-105 may no records such high MTFs like Nikkors do, but it’s more even and excellent at maximum aperture, at which it’s better than Sigma.

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Let’s discuss edge of the frame performance now, which is illustrated on the graph below.

Sigma 18-125 mm f/3.8-5.6 DC OS HSM - Image resolution

Here Sigma comes out noticeable better in comparison to the competitors. Its advantage is even behavior and small differences between individual focal lengths, and also between maximum aperture and other aperture values. It doesn’t beat the very good Nikkor 18-105 mm VR, but it is noticeably better than Nikkor 18-135 mm, what can be observed very well at longer focal lengths. Longer focal lengths, particularly their maximum aperture, are also Sigma’s chief asset compared to Sony 16-105.

So what Sigma lost at the center, it made up for at the edge of the frame. Basically, only Nikkor 18-105 mm VR remained beyond its reach, but it can square up to other lenses of the same class easily. What’s important, the new model of Sigma is generally far better than its predecessor of the same focal length range.

At the end of this chapter we present clippings of our test chart, obtained from JPEG files saved simultaneously with discussed above RAW files.

Sigma 18-125 mm f/3.8-5.6 DC OS HSM - Image resolution