Originally posted by Digitalis
To be completely honest there are highly regarded pentax lenses that can produce migraine inducing bad bokeh, so I would take the sample images with a pinch of salt.
With that in mind, I present this visual atrocity:
(...)
Originally posted by Digitalis
Actually, pretty much any lens can produce that kind of bokeh. At a close focus distance, at wide apertures, under harsh Australian sunlight, with bright specular highlights in the background - Images like that nearly always produce horrible results.The only exceptions to that rule are apochromatic lenses, which due to their superior optical correction are largely immune to producing bokeh like that.
The "
bad bokeh" in the picture you are presenting results from the combination of:
-
Longitudinal chromatic aberrations (non-coinciding focal planes of the various colours), leading to magenta (red + blue) outlining in front of the focus point and green beyond;
-
Coma (aka comatic aberration: off-axis point sources appearing distorted, sort of having a tail like a comet); and
-
Mechanical vignetting (specular highlights in the background taking the form of "cat's eyes" in the corners).
Truly
apochromatic lenses don't show longitudinal chromatic aberrations but can still suffer from coma (
aplanatic lenses don't) and mechanical vignetting.