Lens review

Tamron 17-50 mm f/4 Di III VXD

13 March 2024
Maciej Lata³³o

4. Image resolution

Our resolution test (resolution meaning the MTF50 function values) of Sony FE lenses is based on RAW files from the 42.4 Mpix sensor of the Sony A7R II, the Sony A7R III, or the Sony A7R IIIa cameras. In the case of this kind of detector the decency level we set near 39-41 lpmm and the best fixed focal lenses have been able to reach 75-80 lpmm. The record breaking constructions are able to get to even 90 lpmm. So far, the list of such record breakers has included the Sigma C 65 mm f/2 DG DN (82.7 lpmm), the Sony FE 20 mm f/1.8G (83.7 lpmm), and the Sony FE 50 mm f/1.4 GM (90.9 lpmm).

Let's see how the Tamron 17-50 mm f/4 Di III VXD compares – its results in the frame centre at 17, 33, and 50 mm presents graph below.

Tamron 17-50 mm f/4 Di III VXD - Image resolution

When it comes to the frame centre, several things stick out. First of all, you see noticeable differences between particular focal lengths and image quality decreases with the increase of the focal length's value. Secondly, the performance of the lens is hardly impressive – image quality is good and only good, nothing more. Fortunately the lens doesn't have any weak points in this category either, because even at the maximum relative aperture you land safely above the decency level at any focal length.

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Now let's check how the situation changes as you pass to the edge of the APS-C sensor – an appropriate graph you can find below.

Tamron 17-50 mm f/4 Di III VXD - Image resolution

Here the hierarchy is preserved even though the difference between 17 and 33 mm decreased. Both focal lengths provide a sensible image quality up from the maximum relative aperture. Unfortunately you can't say the same thing about the 50 mm focal length that requires a stopping down to f/5.6 in order to ensure that sensible image quality.

Now the time has come to check the edge of full frame and we admit, for a lens with such original parameters, the bar is raised really high.

Tamron 17-50 mm f/4 Di III VXD - Image resolution

One glance at the graph above and you know that the Tamron didn't manage to jump that bar in many places. First of all the constructors gave up on the maximum focal length – it has problems with reaching the decency level even on stopping down. In case of shorter focal lengths the decency level is not reached at the maximum relative aperture but stopping down the aperture by 1 EV solves the problem. Of course the performance still remains mediocre but, as long as you stick to the aperture range from f/5.6 to f/11.0, you are able to get more or less sharp images across the frame.

At the end of this chapter we would like to present some crops taken from our test photos, saved as JPEG files alongside the RAW files, used for the analysis above.

A7R IIIa, JPEG, 17 mm, f/8.0
Tamron 17-50 mm f/4 Di III VXD - Image resolution
A7R IIIa, JPEG, 50 mm, f/4.0
Tamron 17-50 mm f/4 Di III VXD - Image resolution