Bokeh (from Japanish boke) refers to the blur obtained in pictures far from the focused area. This blur depends on several parameters, which gain in importance in DSLR cameras; among them:
- Sensor size: the bigger it is, more visible is the effect of the lens behaviour on different image zones, from the focusing point to areas far from it. The physics of the lens will trace light rays differently to each specific zone of the sensor. In compact cameras, this effect is very limited due to the small sensor size.
- Lens quality (objectives): The different coatings applied to each specific lens in a given objective to reduce internal reflection will produce more or less defined contours in objects out of focus, allowing (or not) its recognition. Those coatings are responsible (together with glass quality), of the generation of "ghost" contours around objects near the focus range.
- Number of diaphragm blades: This is the most critical topic; DSLR lenses typically use between 5 and 9 moving blades to produce the diaphragm opening, which will allow for more or less light throughput to the camera sensor. The more blades are used, the more circulas shape will be obtained. With just five blades, out-of-focus light points will have pentagonal shape - which may be desired or not. In the sample image, the lens had eight blades, so that octagon shapes can be observed.
Originally posted: Jan 25th 2012 (Over-Blog)