Lens review

Leica Apo-Summicron-M 75 mm f/2.0 Asph

4. Image resolution

The resolution of the tested lens was based on DNG files from a Leica M9. These files were developed without sharpening by dcraw program and saved in TIFF format. After that we analyzed them using Imatest program which allowed us to determine MTF50 values. Measurement errors ranged from 0.3 to 1.8 lpmm. The frame centre and the frame edge results are presented on a graph below.

The Leica Summicron 2/75 is considered to be the sharpest lens of the M system. Its performance in the frame centre confirms that opinion. Instruments with 70-85 mm focal lengths and as fast as f/1.8-2.0 usually fare poorly when wide open. It was true for the Canon EF 85 mm f/1.8 USM and for the Nikkor AF 85 mm f/1.8D, which had to be stopped down to f/2.0-f/2.2 to produce useful images. The Pentax 1.8/77 coped a bit better here, being fully useful even by f/1.8. The Leica is even better than that. The usefulness level for all the lenses tested on the M9 is set at about 34 lpmm. The Summicron 2/75 doesn’t have the slightest problems with exceeding it and, at the maximum aperture, is reaches a good result of 38 lpmm. It gets only better and by f/5.6 the lens achieves the value of 50 lpmm.

When it comes to the frame edge performance we feel a bit dissatisfied, though. According to the producer and MTF graphs, presented in catalogues, we were supposed to deal with fully useful images even near the maximum relative aperture. Unfortunately, observing the situation at the frame edge of the M9 we must say that the level of full usefulness is reached only on stopping down to at least f/4.0.

We must admit, however, that the Pentax 1.8/77, so praised by us, near the maximum relative aperture at the edge of a smaller APS-C/DX frame achieve similar results as the Leica at the edge of full frame. On the other hand, though, the Leica costs four times more than the Pentax so we should expect that it will fare significantly better…

Traditionally, we end this chapter presenting you some photo crops from the frame centre of our test chart. These pictures are JPEG files which were saved along DNG files, used to generate the graph above.