Bokeh

Bandelier National Monument

March 11, 2020

One of basic elements of photography is the concept of depth of field (DOF). It is defined as the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

If you have a recent iPhone with “portrait” mode, you are familiar with depth of field.

Bokeh is the blur or the aesthetic quality of the blur, in out-of-focus areas of an image, or “the way the lens renders out-of-focus points of light. Bokeh comes from the Japanese word boke (ボケ), which means "blur" or "haze", or boke-aji, the "blur quality." Bokeh is pronounced BOH-Kə or BOH-kay.

Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—”good” and “bad” bokeh. Bokeh occurs for parts of the scene that lie outside the depth of field.

DOF is determined by aperture, focal length, and subject distance; the characteridtics of bokeh are a function of the lens.

If you are game, here’s some detail on bokeh:

Bokeh characteristics may be quantified by examining the image’s “circle of confusion.“ (I thought it was just me!). In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. The shape of the aperture has an influence on the subjective quality of bokeh as well. For conventional lens designs (with bladed apertures), when a lens is stopped down smaller than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape formed by the aperture blades. This is most apparent when a lens produces hard-edged bokeh. For this reason, some lenses have many aperture blades and/or blades with curved edges to make the aperture more closely approximate a circle rather than a polygon.

Nikon offers the following tips for achieving good bokeh:

1. Fast aperture is best (at least f/2.8)

2. Use fast prime lenses

3. Long focal length creates more extreme bokeh

4. Shoot lens wide open

5. Increase distance between subject and background

6. Move closer to your subject

7. Take portraits and macro images in nature

8. Use a backlight or side light.

You are now armed to impress your friends who are into photography. 😁🤪🤙