In order to truly understand a concept, we must know the science behind it! Today let's look into "bokeh". Read on and be informed.
The root of the Japanese word “bokeh” is, in effect, negative – often used to describe a “confused” mental state. In photographic terms, bokeh describes the rendition of out of focus points of light. The word “confused” was used because the light beams no longer come together at a single point in an orderly manner. You can even think of it as the “confused” part of a photo. It’s important to remember that bokeh isn’t the out of focus area of the photo itself – it is the character or quality of the out of focus parts of an image and in that way – it, bokeh, is a subjective phenomena.
How does it happen?
Any image is represented by a large number of images of points. An unsharp imaged point is associated with a circle of confusion or a blur disk and a lens produces a circle of confusion which is an illuminated shape directly corresponding to that of the lens aperture. These blur disks are judged by shape, size and the light distribution they receive. The size of the circle of confusion depends upon how far the film is from where that particular detail of the image is focused and if the shape of the aperture is for example a star – the circle of confusion will effectively become a “star” of confusion. The larger the aperture (smaller f-number), the shallower the depth of field, the more prominent the effect appears on the out of focus area in the background.
The characteristics of lenses, including their aberrations must also be taken into account when thinking about bokeh. There are also several variables that affect the appearance and quality of out of focus areas such as picture format, focal length, camera-to-subject distance, distance to the background or the foreground, shapes and patterns of the subject, iris shape, aberrations of the lens, speed of the lens, foreground/background brightness and colours.