Lens review

Pentax smc DA* 55 mm f/1.4 SDM

13 May 2009
Arkadiusz Olech

4. Image resolution

The image resolution of the tested lens has been measured on the strength of RAW files from Pentax K20D. The measuring errors oscillated between 1 lpmm in the maximum aperture range and lessened to 0.3 lpmm for closed aperture.

The results of our test, both for the center and the edge of the frame, are illustrated on the graph below.

Pentax smc DA* 55 mm f/1.4 SDM - Image resolution

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As far as the center of the frame is concerned, we are worried about the fact, that the lens hasn’t reached the level of 30 lpmm at maximum aperture. But, to be honest, neither has the older Pentax 1.4/50, or even Zeiss Planar 1.4/50. Sigma 1.4/50 hasn’t done that as well, but it had the hardest task as it was tested on an 8-megapixel sensor of Canon 20D, and taking this fact into account, we can assume that it performed the best at maximum aperture.

Even slightly stopping down makes all our reasons to complain about Pentax 1.4/55 disappear. The plot goes up very quickly to reach record-breaking result at f/4 and f/5.6, ones only observed with the “cult” Pentax 1.8/77 LTD.

As for the edge of the frame, again, maximum aperture makes us complain a little. The level of 20 lpmm is really low and here even the older Pentax performs somewhat better, along with Zeiss and Sigma. Stopping down by one aperture value doesn’t leave us satisfied yet, as we still don’t reach 30 lpmm.

Another thing to notice when comparing the new and the old Pentax is the fact, that the new model at maximum aperture gives higher overall contrast, that is higher MTF values for 80 or 90% contrast. It manifests in the pictures as the lack of characteristic “mist” that is the domain of the old Pentax or e.g. Canon 1.4/50 USM.

 Generally speaking and taking into account measuring errors, lenses like Pentax 1.4/55, older Pentax 1.4/50, Zeiss Planar 1.4/50 or Sigma 1.4/50 represent similar and high level with slight indication on the two latter instruments. That’s why the choice between them is mainly based on prices. Unfortunately, this isn’t good news for the DA* 1.4/55 tested here, as it’s one of the most expensive. Considering the price we have to pay for it, we have the right to expect better performance at maximum aperture range.

Pentax smc DA* 55 mm f/1.4 SDM - Image resolution