Lens review

Sony FE 50 mm f/1.8

24 November 2017
Arkadiusz Olech

4. Image resolution

The resolution test (resolution meaning the MTF50 function values) of the Sony FE 50 mm f/1.8 was based on RAW files from the Sony A7R II camera. In the case of that mirrorless device the decency level we set about 38-40 lpmm and the best fixed-focal lenses have reached 65- 70 lpmm. The Tokina Fírin 20 mm f/2 FE MF has held the record so far, with a resolution value of 72.6 lpmm.

Let’s check how the tested lens compares – its performance in the frame centre, on the edge of the APS-C sensor and on the edge of full frame presents a graph below.

Sony FE 50 mm f/1.8 - Image resolution

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The performance in the frame centre is typical for simple 1.8/50 constructions. Near the maximum relative aperture the results are on a decency level borderline. Still the resolution increases swiftly on stopping down the aperture (so eliminating different optical aberrations), reaching the peak near f/4.0-5.6 and then decreasing due to diffraction. The performance of the Canon EF 50 mm f/1.8 STM and the Nikkor AF-S 50 mm f/1.8G was almost identical.

Still when you compare the tested lens to another system device with similar parameters, namely the Zeiss Sonnar T* FE 55 mm f/1.8 ZA, you see more differences. The Zeiss is a more complex construction, ensuring you a better image quality in the f/1.8-2.8 range but it doesn’t go as high by f/4.0 and f/5.6.

For obvious reasons the resolution values of the Sony FE 1.8/50 on the edge of full frame are weaker. If you want to enjoy a completely useful image on the edge of the APS-C sensor you have to close the tested lens down to near f/3.2. On the edge of full frame the same effect can be achieved only by applying f/4.0 or so. These results are practically the same as results of the Nikkor AF-S 50 mm f/1.8G, but a bit lower than the performance of the Canon EF 50 mm f/1.8 STM.

One thing is interesting here. Classic 50 mm lenses designed for reflex cameras even out image quality across the frame easier. For example when it comes to the Canon EF 50 mm f/1.8 STM and the Nikkor AF-S 50 mm f/1.8 G it would be difficult to find any significant difference between the resolution in the frame centre and the edge of the APS-C sensor. In the case of the Sony FE 50 mm f/1.8 that difference is distinct. Once again it proves that a small distance between optics and a sensor means not only assets but also measurable drawbacks.

At the end of this chapter, traditionally, we present crops taken from photos of our resolution testing chart, saved as JPEG files along RAW files we used for the analysis above.

A7R II, JPEG, f/1.8
Sony FE 50 mm f/1.8 - Image resolution
A7R II, JPEG, f/4.0
Sony FE 50 mm f/1.8 - Image resolution