Carl Zeiss Touit 32 mm f/1.8 review - Image resolution

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Carl Zeiss Touit 32 mm f/1.8

29 September 2013

Arkadiusz Olech

4. Image resolution

The resolution test of the Zeiss Touit 32 mm f/1.8 was based on RAW files from the Fujifilm X-E1. We developed those files using the old version of dcraw with the VNG demosaicing algorithm. We did it in order to make them directly comparable to the RAWs from the Fujinon XF 35 mm f.1.4 R which were analyzed by that version of software.

The resolution graph of the Zeiss in the frame centre and on its edge is presented below.

Carl Zeiss Touit 32 mm f/1.8 - Image resolution

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As you can see at the maximum relative aperture the Zeiss gets MTFs near 45 lpmm so safely above the decency level, set in this case at 39-40 lpmm. The Fujinon 1.4/35 had some problems with the full usefulness at the maximum relative aperture but it was also faster. If you compare the performance of both lenses by f/2.0 the Fujinon is by almost 4 lpmm sharper. The situation changes by f/2.8 where the Zeiss is better. By f/4.0-5.6 both lenses reach the maximum of their possibilities and get to a very high level of 65 lpmm. By higher aperture values the image quality is limited only by diffraction, not optical aberrations.

The edge of the frame of the Zeiss looks better. You can’t get useful images near the maximum relative aperture but on stopping down to f/2.2-2.5 you can see that problem disappear. In the case of the Fujinon you had to stop down to f/2.8 or even more to enjoy really sharp photos.

As in the future we are going to analyze the Fujifilm X optics using the RAW files developed by dcraw program with a much better 3-pass X-Trans filter algorithm, below you can find the MTFs of the Zeiss 1.8/32 reached with that software.

It is clear that in places of low resolution the improvement, compared to VNG, is slight – after all, in fuzzy images the VNG algorithm artifacts are not so visible anyway. When an image is very sharp the artifacts limit the resolution significantly so their lack in the 3-pass algorithm makes resolution levels increase even by several lpmm. As a result the Zeiss got the maximum MTFs as high as over 72 lpmm.

At the end we present crops taken from JPEG files which were saved along RAW files, used for the analysis above.