Lens review

Sony 50 mm f/2.8 Macro

4. Image resolution

One glance at a curve, showing the relationship between MTF50 function values and the aperture values in the frame centre (by the way of reminder MTFs are measured on the strength of unsharpened TIFF files converted from RAWs of the Alfa 100 using dcraw program) gives us the first pointer to why the price of the 2.8/50 model is so high. Within an accuracy of the margin of error the image is the sharpest by f/2.8 and f/4.0 so in the proximity of the maximum relative aperture, reaching the level of 42-44 lpmm. Constructing a lens which wide open reaches its maximum (and very high to add) resolution level is no mean feat. In the case of the Sony 2.8/50 that much was achieved without any doubt, though.

The situation at the edge of the field is worse but only because you can hardly reach such high MTFs near borders as in the centre. The tested lens can’t be blamed for that, quite the opposite in fact, it deserves our praise.

One thing that might stick out and also surprise a bit is slight fluctuation on the MTF50 graph near f/4.0. It is not an effect of a measurement error because that fluctuation was noticed in test charts of different sizes during two different test sessions. On the other hand we must state clearly that our measurement errors in the case of this test and for values, measured near the maximum relative aperture, amount to about 1.0-1.5 lpmm. Such an error is slight because it just reaches the level of 2-4%. It is, however, big enough to allow the measurements by f/2.8 and f/4.0 to overlap each other even if you implement the 1-sigma criterion. From the statistical point of view the fluctuation on the graph is insignificant. Fortunately from the practical point of view it is also negligible as both values, 42 and 44 lpmm, are still very high.