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Lens review

Viltrox PFU RBMH 20 mm f/1.8 ASPH

20 May 2019
Arkadiusz Olech

5. Chromatic and spherical aberration

Spherical aberration

Three elements made of low dispersion glass perform as they should and correct chromatic aberration well so we have no reservation in this category. The photos below show very clearly that longitudinal chromatic aberration is barely visible even at the maximum relative aperture.

Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration

Good news also concern lateral version of this aberration and our results presents a graph below.

Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration


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On both types of detectors the aberration keeps a constant level which can be placed on the borderline between low and very low values, no matter what aperture value you employ so you should't worry about it at all. In this category the Vlitrox has a tad better results than the more expensive Tokina as its aberration could reach even about 0.08% for some combinations of apertures and positions in frame.

A7R II, RAW, APS-C, f/1.8 A7R II, RAW, FF, f/4.0
Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration

Spherical aberration

First photos of this chapter don't show any 'focus shift' symptoms so spherical aberration level can't be high or very high. Still, defocused circles of light are the proof that it is not corrected in a perfect way either. They are different: the circle before the focal point has a distinctly darker centre than the circle behind the focal point.

A7R II, f/1.8, in front of A7R II, f/1.8, behind
Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration Viltrox PFU RBMH 20 mm f/1.8 ASPH - Chromatic and spherical aberration