Fujifilm Fujinon XF 35 mm f/1.4 R
5. Chromatic and spherical aberration
Fast lenses with moderate focal lengths have often quite noticeable problems with the longitudinal chromatic aberration. The tested Fujinon is not an exception here. That aberration is visible both at the maximum relative aperture and on stopping down to f/2.0. Its level is perhaps not exceptionally high but you can notice it in many situations.
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The lateral chromatic aberration is low near the maximum relative aperture. On stopping down the lens to apertures higher than f/2.8 that aberration increases to medium values. The monotonic increase of chromatic aberration along with stopping down the aperture is one of the factors which make the resolution increase on the edge of the frame more sluggish than it should be. On stopping down other off-axis aberrations decrease but the lateral aberration increases, lowering the MTF50 values for one of the coordinates.
It’s worth adding here that the graph, presented above, shows the performance on RAW files. In the case of JPEG files the Fujifim X-Pro1 corrects that aberration partially so the numerical values are about two times lower.
The Fujinon XF 35 mm f/1.4 R is not completely free of spherical aberration – it can be seen very clearly in the photos of a defocused diode.
The light spread in the circle is not even – in both cases we see a distinct ring, lighter behind the focus, darker in front of it. Fortunately the spherical aberration can be felt only near the maximum relative aperture which means that only the extreme elements of the optical system contribute to it. There is no “focus shift” effect (look at the photos of our autofocus chart, presented in this chapter) and the light ring disappears by higher aperture values (look at defocused images of a diode in chapter 7)