Tamron 28-75 mm f/2.8 Di III RXD review - Image resolution

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Tamron 28-75 mm f/2.8 Di III RXD

26 August 2019

Arkadiusz Olech

4. Image resolution

The resolution test (resoltuion meaning the MTF50 function value) of the Tamron 28–75 mm f/2.8 Di III RXD 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 could 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 Tamrona 28–75 mm f/2.8 Di III RXD compares – its performance in the frame centre at 28, 50, and 75 mm, presents a graph below.

Tamron 28-75 mm f/2.8 Di III RXD - Image resolution

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The performance at the shortest focal length is simply sensational! Already at the maximum relative aperture you deal with a very high resolution, that of 66 lpmm, and after stopping down the aperture to f/4.0 it increases further to a fantastic value of over 74 lpmm. So far, these results have been available only in the best system primes!

In the middle of the focal length range the situation is just slightly worse. At the maximum relative aperture the results keep an excellent level of 65-66 lpmm; on stopping down the aperture MTF's don't exceed 70 lpmm but I must observe a level over 68 lpmm would be a dream come true for many fixed focal length instruments with the Zeiss logo on their barrel.

The performance at 75 mm in the aperture range from f/4.0 to f/22 is practically indistinguishable from levels we observed in the middle of the focal length range. We noticed a resolution crisis for a combination of 75 mm and f/2.8 as the lens got just 49 lpmm and that result lags behind the rest. Still it is firmly above the decency level so here the lens doesn't deserve to be criticized even a bit.

Now let's check how the Tamron 28-75 mm manages to perform on the edge of the APS-C sensor – an appropriate graph you can find below.

In this case the 50 mm focal length rise well above the rest. Even at the maximum relative aperture the results are sensible and after stopping down the aperture the MTFs increase to about 55 lpmm.

Unfortunately both ends of the focal length range fare weaker. In their case the maximum relative aperture means results on the borderline of the decency level; even a significant stopping down doesn't allow them to exceed 50 lpmm. What about the demanding edge of full frame? Let's look at the graph below.

Regrettably, once again there are no reasons to smile. The graphs are quite flat, the results keep well below 40 lpmm and the decency level is achieved only near f/5.6 – 8.0 but these are marginal cases.

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

A7R II, JPEG, 28 mm f/4.0