Bokeh and the circle of confusion

Photographers spend an extraordinary amount of money and effort in trying to get pin-sharp images that are exactly in focus. They agonize about whether auto-focus lenses get fooled by various elements in the picture like bright colors (especially yellow) which cause the auto-focus mechanism to focus slightly behind the image, rendering the image slightly fuzzy. They buy ever more expensive lenses looking for that elusive sharpness in the image.

But there is a whole art form hidden in the part of the picture that is out of focus. You may have noticed that out-of-focus specular highlights (like sources of light or shiny objects) in images devolve into circles of confusion. The shape of the circle of confusion created by an out-of-focus object depends on many things - the number of blades in the lens iris (more blades equals a more rounded circle of confusion), the focal length of the lens (longer lenses create more smooth circles of confusion) and of course the quality of the glass itself.

Other than the rather long-winded and pedestrian term 'circle of confusion' we really don't have a good way to describe the quality of the out of focus part of the picture. The Japanese on the other hand have done a considerable amount of study into the quality of the out-of-focus part of the image and even have a term for it: they call it 'Bokeh'.

For the discerning photographer, there is now a range of lenses from each of the major manufacturers the gives you excellent bokeh. The kind of creamy soft out of focus images that are used in the new movies.

I find the aesthetic of bokeh fascinating, and I offer you this picture as an example of very good bokeh.