'Bokeh' is a Japanese word that simply means blur or haze. It refers to out of focus area in a photograph. To keep the subject in focus and the background out of focus is a popular technique among photographers and it is used to isolate the subject and make the photograph more appealing.
In this article we will try to understand what depth of field means, what factors affect it and how to use it to create beautiful images.
Depth of field refers to the range of distance from the camera which is sharp in focus in an image.
If depth of field is 1 meter starting 2 feet from the camera then anything which is nearer than 2 feet and farther than 1 meter 2 feet will be out of focus or blurred. Only subjects within the 1 meter range starting 2 feet from the camera will be sharp in the image. So in nutshell you may remember that Depth of Field (DoF) refers to region in focus and 'Bokeh' refers to region out of focus.
DoF depends on three factors; aperture, focal length & distance of the subject from the camera and also the distance of the background from the subject. As aperture gets wider, depth of field gets smaller. At F/1.4 aperture depth of field is razor thin, specially close to the camera. Higher F numbers (F/8 or F/22) tend to produce a very wide depth of field which is desired for landscape photography. It means everything, starting few feet from the camera and all the way to very far away, will be sharp in the image.
Wide apertures (smaller F numbers) also cause an effect called shallow depth of field. Depth of field means the width of the area which is going to be sharp in the image. For example if depth of field is 1 meter starting 2 feet from the camera then anything which is nearer than 2 feet and farther than 1 meter plus 2 feet will be out of focus or blurred in common language. Only subjects within the 1 meter range starting 2 feet from the camera will be sharp in the image. As the aperture gets wider depth of field also gets smaller. At F/1.4 aperture depth of field close to the camera is razor thin.
Since wide aperture allows more light to get in the camera, lenses with wider apertures allow faster shutter speeds and hence also called fast lenses.
It’s difficult to maintain optical qualities uniform throughout the lens surface area in an arrangement of various glass elements, therefore, lenses with very wide apertures are also very expensive. Wide aperture lenses are preferred for portrait photography.
Higher aperture numbers (F/8 or F/22) means smaller opening and have a very wide depth of field which is desired for landscape photography. It means everything from very close to the camera and all the way to very far away everything will be sharp in the image.
Picture tends to get softer at F18 and higher numbers due to diffraction phenomenon. Star rays effect can be achieved from bright objects at very high F numbers such as F22 or F30.
Aperture also controls the depth of field in a photograph.