![]() Spherical aberration will cause light to be unevenly distributed within the cone and produce different intensity across the circle and, when attempts are made to correct it, they often compound the problem instead of solving it.Ĭhromatic aberration (particularly longitudinal CA) can produce rings around the boundaries of blur circles. Real lenses are never perfect (although some can come close). In a perfect lens, blur circles should have sharp edges and even illumination. ![]() (75-300mm lens at 210mm f/5.6 on camera with an APS-C-sized sensor.) Even though the subject was many metres in front of the tree behind, the contrasty background could not be defocused enough at the aperture used to produce smooth bokeh. The diameter of the cone of light at the point where it becomes a disk instead of a point is known as the ‘circle of confusion’ or ‘blur circle’.Ī harshly-lit background created the choppy bokeh seen in this image. When the apex (point) of the cone falls upon a pixel in the sensor, the image is focused when it falls short of or beyond the sensor, it is out-of-focus. The base of this cone is the lens aperture, which can be adjusted to produce exit pupils of different areas. Each picture element (pixel) is generated when the beams of light passing through the lens aperture combine to form a light cone. To understand bokeh you need to know a little about how images are formed so this section will be a bit technical. You can also change your shooting angle to ensure bright highlights are excluded from the background because large contrast differences can make the bokeh appear ‘choppy’. ![]() Filling the frame with the subject is the most straightforward. There are a couple of ways to minimise the influence of potentially unattractive bokeh. When the blurred background elements take your eyes away from the subject of the photograph, the bokeh is classed as poor. In principle, the best bokeh appears when the subject of the photograph dominates and the bokeh literally ‘retreats into the background’ and is unobtrusive. Similarly, a lens with relatively indifferent bokeh can produce attractive-looking pictures when the background to the subject is evenly lit with soft and harmonious tones. So can tonal relationships with respect to foreground and background brightness and colours within the subject.īackgrounds containing patches of brightness and darkness or strongly contrasting colours can become ‘busy’ looking, even with lenses that normally produce attractive bokeh. The image format, lens focal length, selected aperture, camera-to-subject distance, position of the subject within the scene, and shapes and patterns within the subject can also influence bokeh quality. Differences in aperture shapes and lens aberrations can cause some lenses to blur out-of-focus areas in a way that pleases the eye, while others will produce blurring that is distracting or unattractive. The lens plays a vital role in determining how smoothly background tonality is rendered. The appearance of the background blurring can affect viewers’ perceptions of the attractiveness of a photograph. Background regions become out-of-focus as a result. In most cases, this is achieved with a wide lens aperture, which creates a relatively shallow plane of focus. In all these situations, the photographer will normally use a shallow depth of field to focus the viewer’s attention on the subject by blurring the background. Bokeh can also be important for portrait photography where medium telephoto lenses (typically 85″“150 mm in 35mm format) are generally used. This is easier to achieve with long telephoto lenses but is also an essential parameter in macro photography. (70-300mm lens at 300mm f/8 on a ‘full frame’ camera body.)īokeh is generally associated with a shallow depth of field. Use of a long focal length and a wide distance between the subject and the background ensures attractive bokeh in this shot, even though it was taken with an aperture of f/8, a full stop down from the maximum aperture of the lens.
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