In optics, chromatic aberration (CA, also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the ...
I saw an earlier question (Why prefer the 18-55mm and 55-250mm lenses vs 18-200mm?) that mentioned lower quality lenses have distortion, aberration and light fall off issues. Has software like Adobe ...
http://www.kenrockwell.com/pentax/35mm/lenses/50mm-f17-smc-m.htm After the chromatic aberrations that I observe, it could be an achromat.