Lens review

Sony FE 85 mm f/1.8

15 March 2019
Arkadiusz Olech

4. Image resolution

The resolution test (resoltuion meaning the MTF50 function value) of the Sony 85 mm f/1.8 FE was based on RAW files from the Sony A7R II camera. In the case of that mirrorless device the decency level we set about 39-41 lpmm and the best fixed focal length lenses have been able to exceed 70 lpmm. So far, the Tokina Fírin 20 mm f/2 FE MF (72.6 lpmm) and the Voigtlander Apo-Lanthar 65 mm f/2 Aspherical 1:2 Macro (78.5 lpmm) have been the record holders.

Let’s check how the tested Sony 85 mm f/1.8 FE 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 85 mm f/1.8 - Image resolution

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The image, presented here, seems to be in accordance with our expectations; the results are typical for a slightly improved lens of the older type. Classic constructions have always had problems with exceeding the decency level at the maximum relative aperture but the Sony manages to do so with ease. Still it fares just moderately well, without any fireworks. By f/2.0 the resolution is even a bit better, reaching 49 lpmm but it is also by as much as 10 lpmm lower than the result of the Sony FE 85 mm f/1.4 GM. A similar advantage of the more expensive model is noticeable also by f/2.8 and only by f/4.0 it decreases to less than 2 lpmm.

The peak of performance the Sony FE 85 mm f/1.8 reaches by f/5.6 where it is able to reach 66.5 lpmm. It is a very good level but far from any resolution records – these seem to be firmly reserved for new constructions.

The edge of the APS-C sensor sticks out from the results in the center but, on the other hand, there are no distinct weak spots. Even by f/1.8-2.0 you deal with a decent image quality and on stopping down the aperture you are able to improve it further.

Weak points, however, are visible on the edge of full frame. Close to the maximum relative aperture it would be difficult to call image quality sensible. In order to enjoy decent MTFs you have to stop down the lens to a value of f/5.6. Once again the cheaper model has to admit its defeat in a duel with the more expensive Sony 1.4/85 GM which was able to provide fully useful images already from about f/1.8.

To sum up we still don't doubt that the Sony FE 1.8/85 is a very sensible alternative to its faster but three times more expensive brother. After all it ensures sharp, completely satisfying images in the frame centre and on the edge of the APS-C sensor. However, if you really care about a distinctly better performance in the f/1.8-2.8 range, a sharper edge of the frame and the advantages provided by the f/1.4 aperture you have to spend more and buy the more expensive model; the cheaper one simply won't satisfy you.

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

A7R II, JPEG, f/1.8
Sony FE 85 mm f/1.8 - Image resolution
A7R II, JPEG, f/5.6
Sony FE 85 mm f/1.8 - Image resolution