Carl Zeiss Touit M 50 mm f/2.8 review - Chromatic and spherical aberration

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Carl Zeiss Touit M 50 mm f/2.8

12 November 2014

Arkadiusz Olech

5. Chromatic and spherical aberration

Chromatic aberration

The longitudinal chromatic aberration is not corrected in a perfect way and the photos, shown below, are the proof. The image behind the focal point is slightly yellowish and that in front of the focus comes with a greenish-blue cast.

Carl Zeiss Touit M 50 mm f/2.8 - Chromatic and spherical aberration

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I admit we are a bit surprised by such a result. The construction of the lens consist of as many as 14 elements and two of them are made of low dispersion glass. The lens is not exceptionally fast either and it was made by a reputable producer. In our view the aberration performance should have been a bit better.

Unfortunately the lateral chromatic aberration must be described in a similar way; the graph, showing a correlation between it and the aperture values is shown below.

You don’t have to worry when you operate near the maximum relative aperture but when you stop down the lens that aberration increases quickly and in a range from f/8 to f/22 it comes near a high level. I don’t understand such a move. To be completely honest I would prefer it the other way round – the aberration could have been higher near f/2.8 as it would disappear in the blur anyway. In the macro range, where the lens is stopped down quite significantly, the “colouring” on contrasting edges is definitely not something you would like to see.

Spherical aberration

The lens didn’t have any „focus shift” effect. Images of defocused light points we got in front of and behind the focus didn’t differ in a significant way. Both these facts make us think that the Touit corrects the spherical aberration in a proper way.