Lens review

Pentax smc DA 50 mm f/1.8

22 December 2012
Arkadiusz Olech

4. Image resolution

The resolution test of the Pentax smc DA 50 mm f/1.8 was based on RAW files from the Pentax K-5 reflex camera. In that case the best “primes” can reach results as high as 52-53 lpmm and the decency level is situated near 34-35 lpmm. Let’s check how the tested lens compares here. A graph, presented below, shows its achievements in the frame centre and on the edge of the APS-C/DX sensor as well.

Pentax smc DA 50 mm f/1.8 - Image resolution

At the maximum relative aperture and by f/2.0 the images are not completely useful but it is hardly a surprise – few 1.8/50 instruments are useful there. In fact the Pentax fares very similarly as its competitors. On stopping down the quality of images improves fast. By f/2.8 the resolution is already on a good level and by f/4.0 it becomes excellent and by f/5.6 – sensational. When it comes to the performance in the frame centre you can boldly say you deal here with a very well-designed system of the 1.8/50 class.

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It is worth mentioning one more thing. Our resolution measuring fields are situated not exactly in the frame centre but more than a dozen percent away. In the case of the Pentax it does matter a lot because the resolution of the tested model decreases swiftly as you move away from the geometric middle of the frame. In the very middle the MTFs are noticeably higher than the values shown on our graphs near 30 lpmm.

You can talk about the performance on the edge of the frame in similar terms. Near the maximum relative aperture the images are not especially useful but from f/2.8 onwards they become fully acceptable and from f/4.0 we can call them good with clear conscience.

Traditionally at the end of this chapter we present crops of our testing chart, taken from JPEG files (the lowest sharpening level) saved along RAW files, used for the analysis above.

Pentax smc DA 50 mm f/1.8 - Image resolution