Pentax smc DA 50 mm f/1.8
5. Chromatic and spherical aberration
Chromatic aberration
When it comes to the longitudinal chromatic aberration the tested Pentax is not entirely free of it. A slight colouring of images before and after the focus is noticeable at the maximum relative aperture and also on stopping down by 1 EV. Fortunately this effect is not especially pronounced.
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The lateral chromatic aberration is corrected exceptionally well for a change. Its level is very low near the maximum relative aperture and literally zero after more significant stopping down. Here the Pentax deserves a round of applause.
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Spherical aberration
The lens didn’t show any focus shift symptoms so in this regard the spherical aberration is not bothersome. Still it is not corrected in a perfect way as you can notice looking at defocused light points. In front of the focus the circle has a noticeably lighter middle. When you move away from it the light intensity decreases and on the very edge it passes into a noticeably lighter rim. The image behind the focus has a more even light spread although also in its case you can notice rings near the very edge.
