A NOTE ON BOKEH
A topic of the Wise and Wonderful Web is the pseudo Japanese term bokeh, the scent of a lens. Bokeh is a function of the way spherical aberration is corrected and is one aspect of the overall quality of a lens, its drawing. These drawing qualities include sharpness, the beneficial affect of flare on shadow detail, field curvature, distortion and everything. What marks a great lens design is the balance of its corrections.
Bokeh, or boke-aji translates as “blur quality”, but literally means “flavour of haze”. I am told the Japanese have a habit of shortening whole phrases to single words particularly if there is a pun or double entendre to be had, so it collapsed in to just “boke”, which refers to the appearance of the parts of the image that are out of the depth of sharp focus
I use ancient screw mount Leicas for snapshots and recording ideas and events. I find the Cosina/Voigtlander 35mm f2.5 lens to be one of the very best in terms of the smoothness of the unfocused areas in front of as well as behind the plane of focus
In Photographic Lenses, Conrad Beck and Herbert Andrews, pub London circa 1905 I came across the first sensible description of bokeh (see pic)Good boke-aji is represented by 160 B, where the brightness of an out of focus patch of light fades out at the edge