Bokeh Explained

AbelCine gives an explanation of what bokeh is along with a demonstration of the effect when using three different lenses. They say, "The bokeh of a lens defines how that lens renders the out of focus portions of the image. In representing a three-dimensional space on the two-dimensional field of a photographic plate, the geometry of the path light takes through the lens elements can become apparent."

Read more here and see the demo, using the Zeiss Ultra Prime 50mm T1.9, Cooke 50mm S4 T2, and a 60-year old Cooke Speed Panchro Ser.II T2.3 lens, below.