LensTip.com

Lens review

Tamron 20 mm f/2.8 Di III OSD M 1:2

27 March 2020
Maciej Latałło

5. Chromatic and spherical aberration

Chromatic aberration

The parameters of the tested Tamron didn't suggest any serious problems with longitudinal chromatic aberration and indeed, there are no problems at all. Even at the maximum relative aperture and in out-of-focus areas positioned further in the frame it would be difficult to notice any distinct colouring.

Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration


The graph below shows that there are no reasons to worry about lateral chromatic aberration either.

Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration


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Near the maximum relative aperture its level is very low and it increases to values of about 0.06% on stopping down. These results are similar for both types of detectors.

A7R II, RAW, f/2.8 A7R II, RAW, f/11.0
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration


Spherical aberration

The tested lens experiences some problems with spherical aberration. Both tests, performed by us in order to diagnose that aberration, showed that it influences image quality. Firstly, you can notice a slight focus shift on passing from f/2.8 to f/4.0. Secondly, defocused circles of light we got before and after the focus differ from each other – one of them features a distinct, lighter rim.

A7R II, f/2.8, before A7R II, f/2.8, after
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration Tamron 20 mm f/2.8 Di III OSD M 1:2 - Chromatic and spherical aberration