Bokeh describes the rendition of out-of-focus points of light.Basically, bokeh is the quality of out-of-focus or “blurry” parts of the image rendered by a camera lens.

So, how do you get a good bokeh in your images?

Do you know if your lens produces good bokeh? Try this: focus on an object from a very close distance (as close as the lens will allow, keeping the object in focus), making sure that there are no objects at least 5-6 feet behind it. Make sure to be on the same level as the object itself, so that you are not looking down on it. Do not use a plain wall as your background – try to find a colorful background, preferably with some lights on it. A Christmas tree is a perfect background for a bokeh test.

Remember, bokeh is rendered by the lens, not the camera. Different lenses render bokeh differently due to unique optical designs. Generally, portrait and telephoto lenses with large maximum apertures yield more pleasant-looking bokeh than cheaper consumer zoom lenses. For example, the Nikon 85mm f/1.4D lens produces exceptionally good-looking bokeh, while the Nikon 18-135mm f/3.5-5.6G DX lens produces poor bokeh at the same focal length and aperture – all due to differences in optical designs of both lenses.

Canon EF 24-70mm f/2.8L USM Zoom Lens for Canon SLR Cameras

Once you find a good test subject with a suitable background, set your camera to “Aperture Priority” mode and set your aperture to the lowest number. On most consumer zoom lenses, the lowest aperture is typically f/3.5, while on prime and professional zoom lenses, it can be between f/1.2 and f/2.8. Once the aperture is set to the lowest value, take a picture of your subject and take a look at the rear LCD of your camera. The subject should be in focus, while the background is blurred. If you have a good lens, the bokeh should be soft and fuzzy, looking pleasing to the eye as shown in the example above. The circular reflections should be round and soft, with no hard edges.

History of the Term “Bokeh”

So you may ask:  How did such an unusual word, “Bokeh” come to describe the quality of an image’s out of focus area. Well, good question! It turns out that bokeh is coined from the Japanese word “boke” and “boke-aji”, which roughly translate to “fuzzy”  and “flavor of blur”, respectively.  The term was adopted into the English photographic lexicon by Mike Johnston, who currently runs the Online Photographer blog and was previously editor-in-chief for “Photo Techniques” Magazine in the late 1990’s. To give credit where credit is due, Johnston first learned of the term “bo-ke” from Oren Grad, a guy who has multiple graduate degrees (MD’s, PhD’s, and several masters degrees…a genius of sorts) and purportedly learned Japanese just to be able to read Japanese photo magazines! Awesome! The term boke-aji had already been used for some time in Japanese magazines in describing an image’s out-of-focus qualities. In reality, the term bokeh does not translate literally into one meaning in English. In the Japanese literature, there are many shades of the meaning of bokeh, but all boil down to some version of “blur quality.” Johnston was ultimately responsible changing the spelling from “boke” to bokeh to address proper pronunciation, and he popularized the term through a series of 3 commissioned articles on the topic, which were published in March and April 1997 issues of “Photo Techniques”. It was stressed that pronunciation was “bo” as in bone and “ke” as in Kenneth. So that’s how you say it.

The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor. In combination with variation of shutter speed, the aperture size will regulate the film’s degree of exposure to light. Typically, a fast shutter speed will require a larger aperture to ensure sufficient light exposure, and a slow shutter speed will require a smaller aperture to avoid excessive exposure.

http://www.wikipedia.org

The basics

The pupil is the aperture of your eye and, like your pupil, the aperture of a camera lens can be varied in size to let more or less light in. The first basic concept of aperture to get your head around is that the smaller the number [f/1.4 for example] the bigger the aperture, or ‘hole’.

Diagram of decreasing aperture sizes (increasing f-numbers) for “full stop” increments (factor of two aperture area per stop)

A device called a diaphragm usually serves as the aperture stop, and controls the aperture. The diaphragm functions much like the iris of the eye – it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field, which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus.

The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter. A lens typically has a set of marked “f-stops” that the f-number can be set to. A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor. The photography term “one f-stop” refers to a factor of √2 (approx. 1.41) change in f-number, which in turn corresponds to a factor of 2 change in light intensity.

In the old days, cameras had a ring on the lens to change aperture. That ring was marked off in ‘one stop’ gradations:

1.8 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 and so on, but usually not much past f/32 on even the best lenses.

Aperture priority is a semi-automatic shooting mode used in cameras. It allows the photographer to choose an aperture setting and allow the camera to decide the shutter speed and sometimes ISO sensitivity for the correct exposure. This is sometimes referred to as Aperture Priority Auto Exposure, A mode, Av mode, or semi-auto mode.4