CREATING BOKEH
Jon Tarrant explains the various ways in which background effects can be created using aperture selection and lens accessories
Jon Tarrant’s pictures first appeared in AP more than 30 years ago promoting his one-man exhibition at The Camera Club in central London. He has written several books and numerous articles for a variety of photographic publications.
Face-recognition modes that allow AF systems to identify people in pictures are based on a simple general rule: the most important part of a picture should always be fully sharp. If there are people in the picture then they are generally the most important feature and the AF system therefore prioritises those areas. Of course, there are times when this rule can be broken to great effect and there is nothing wrong with a foreground person being out-of-focus, or even in silhouette, if this provides good framing for the scene beyond.
There are many factors that are considered when choosing lenses but rarely do they include the rendering of out-offocus areas. Most of the time, as face recognition algorithms prove, we are more concerned with the things that are in-focus than the areas that aren’t. This is a shame because the out-of-focus quality of an image, commonly known as bokeh, can add to a photograph’s overall effect if it is handled well.
Bokeh is specifically the softness that occurs away from the plane of sharp focus. Although it is most commonly associated with background elements, bokeh refers to the overall appearance of all the out-offocus areas in a photographic image and is often a hard-to-define quality that gives one lens greater appeal over another. The most common bokeh signature is soft circular highlights but its true potential only becomes apparent when considering ways in which it can be manipulated to produce other effects.
One of the prime factors that affects bokeh is the design of the lens aperture and the manner in which its size is changed to allow different amounts of light to pass through in order to achieve the correct exposure. Multiple overlapping blades are pulled completely into the lens housing at maximum aperture then slide together as the aperture size is reduced. The shape of a stopped-down aperture is therefore a polygon and it is often the case that using a larger number of blades, to give a more circular opening, will give better bokeh. This is because the out-of-focus areas of a picture echo the shape of the aperture and few-sided polygons tend to look more intrusive than shapes that have a more circular perimeter.
Old lenses may have as few as five blades but seven is more common and
