Lens review

Sony DT 50 mm f/1.8 SAM

20 May 2009
Arkadiusz Olech

4. Image resolution

The image resolution of the tested lens has been measured on the strength of RAW files from Sony A100, converted to TIFF with no sharpening, using Imatest software. As Nikkor 1.8/50 has been tested on Nikon D200, which also has a 10-megapixel sensor, the results of the lenses can be directly compared. Canon 1.8/50 II has been tested on Canon 20D where the pixel density is lower. If we want to compare the results fairly, we need to raise Canon’s results by roughly 10%. It’s worth to add, that our measuring errors oscillated between 0.5 and 1.8 lpmm.

Let’s have a quick glance at our resolution graph, on which red dots show the center and the blue ones the edge of the frame performance.

Sony DT 50 mm f/1.8 SAM - Image resolution

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The bound of decency is set at 30 lpmm by us. If the lens crosses it at maximum aperture, there’s a reason to praise it. Sony DT 50mm f/1.8 doesn’t do it. MTF50 values recorded at f/1.8-2.0 oscillate in the range of 27-28 lpmm. Should we criticize the Sony lens for that, then? I don’t think so. Firstly, there’s not much missing from those 30 lpmm. Secondly, neither Canon nor Nikkor reach this level, so the behavior of Sony is typical for this class.

The things we can complain about are the values at f/2.8 and f/4.0. Although images at those apertures are very sharp, the competing Nikkor records 4-5 lpmm higher results. Fortunately, at f/5.6 Sony achieves results worthy of a good fixed focal length.

As far as the edge of the frame is concerned, Sony can be praised the most. At maximum aperture range the lens comes off better than both Canon and Nikon. After slightly stopping down, images become entirely useful, and after stopping by 2 EV even very sharp. Sony DT 50mm f/1.8 SAM has no reason to feel worse than more expensive fixed focal length lenses.

To end this chapter, we present picture clippings of our test chart, obtained from JPEG files captured simultaneously with RAW files, used for measuring resolution.

Sony DT 50 mm f/1.8 SAM - Image resolution