Good Bokeh

Bokeh–you know, the fuzziness of the background in an image with small depth of field. Not all lenses have as pleasant bokeh as others. What defines good or bad bokeh? A lens with “good” bokeh generally has two characteristics: round and evenly lit circles of confusion. The roundness is a factor of the number and geometry of the aperture blades. A telling measurement of the evenness of the circles is how closely the sagittal and meridional curves track each other. Here is the MTF chart for the Nikon 85mm f/1.4. Notice that the curves track each other fairly closely. Not surprisingly, this lens is well known for its bokeh. Also, keep in mind as you are trying to achieve the shallowest depth of field that most lenses are sharpest within two stops from maximum and minimum apertures. So, if you find your f/1.4 lens is a little soft, shoot at f/2.8 for best overall sharpness.