Bokeh, from the Japanese word for “Blur”, refers to the image quality of the area of a photograph that is out of focus. Often, the best way to make a subject stand out, is to make the background blurred. To do this, we want to make the depth of field as shallow as possible while still keeping the main subject in focus. The depth of field is directly related to the aperture. The set of pictures below shows how changing the aperture effects the depth of field. While keeping the focus set on the lamp shade, the Christmas lights in the background changes focus depending on the aperture. At f/1.8, the Christmas lights in the background are so out of focus that they appear to be round lights. At f/22, the Christmas tree is almost in focus.
You may notice that in some of the pictures the Christmas lights appear to be pentagons. This is particularly visible at f/4.5. Because the lens used to take these pictures (Canon EF 50mm f/1.8 II) has only 5 aperture blades, the out of focus light forms these pentagon shapes. More expensive lenses often use more aperture blades or rounded edges on the blades to make this appear more rounded giving a more pleasant bokeh.
| F/1.8 |  |
| F/4.5 |  |
| F/8 |  |
| F/11 |  |
| F/16 |  |
| F/22 |  |
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