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Bokeh

Bokeh is a Japanese word that describes the quality of the out-of-focus area in a photograph. Simply being out-of-focus doesn't by itself insure good bokeh, as bokeh is the quality of the out-of-focus area. What constitutes good bokeh is highly subjective, but it's commonly agreed that good bokeh has:

  • a smooth background, with no background patterning.
  • transitions that have soft, rather than sharp edges.
  • light patterns that occur in the background are round in shape with soft edges; not hexagonal or donut shaped, or sharp edged.

A lens can produce out-of-focus areas by controlling depth-of-field, but this does not necessarily produce good bokeh. Bokeh requires an out-of-focus background, but good bokeh requires a lens that can produce a high quality background. Some examples:

This is an example of bokeh at it's worst. The background has what looks like a texture or pattern to it - which almost hurts the eye. And the shapes of the plants in the background have harsh-sharp edges. And although it might be hard to see, the bright-spots have hexagonal-like flat-spots around the edges. This photo was taken by a rather cheap Nikon AF-D 35-80mm f/4~5.6 Macro lens.

Better Bokeh, but still room for improvement. The texturing is gone, but the background still has a hint of harshness in the transitions, and the highlights have some hexagonal flat spots in them. This photo was taken by a Nikon AF-S 18-105mm f/3.5~5.6 VR lens.

This is an example of good bokeh, often called "Cream Cheese Bokeh". As you can see, the background is completely subdued, and creamy... like cream cheese. This photo was taken with a Nikon AF-D 80-200mm f/2.8 lens.

This is another example of good bokeh backgrounds having point-light sources, often called "Hollywood Bokeh". The light sources have blurred rather than sharp edges, and do not have donut like intensities. This photo was also taken with a Nikon AF-D 80-200mm f/2.8 lens.

This is perhaps the worst bokeh I have ever seen. Just the light reflecting off the leaf tips causes "donut" light patterns. This photo was taken with an el cheapo Rokinon 500mm f6.3 mirror lens. No, I don't use this lens. While good bokeh is subjective, I don't think there is any doubt when you see bad bokeh.

 

Conclusion

Bokeh is chiefly dependent on the lens. While this too is highly subjective, it is generally agreed that lenses having 9 or more leafs in the aperture diaphragm, or those with rounded diaphragms produce better bokeh. However, other factors may have a part in good bokeh. Sometimes, one particular lens just produces better bokeh, merely by luck-of-the draw as all of the necessary items line up like the planets. So in some sense, a lens model that has better characteristic bokeh just has that reputation among photographers.