Q: What's bokeh, and how do I get it?
A: Bokeh refers to the out of focus areas of an image. "Good bokeh" means the out of focus (OOF) areas have a pleasing appearance. "Bad bokeh" means these areas do not have a pleasing appearance.
"Bokeh" is not the same as "shallow depth of field."
Many people get confused about the relationship between shallow depth of field and bokeh. Depth of field refers to how much of an image appears to be in focus. When shooting stopped down, especially with hyperfocal settings, depth of field may be tremendous, spanning from just a few feet in front of the lens out to infinity. But when shooting wide open, depth of field may be very shallow, with only inches or millimeters appearing in focus.
Faster lenses (lenses with larger maximum apertures, like a 50mm f/1.8) will allow you to achieve shallower depth of field than slower lenses (such as the kit lens, which goes no faster than f/3.5). However, a faster lens does not necessarily have better bokeh. This is a common confusion, arising from the fact that images with shallow DOF may have large areas which are out of focus. But that does not mean that the out of focus areas are pleasingly rendered.
Bokeh is subjective
Bokeh is subjective. What goes into making the OOF areas look good may vary from photographer to photographer, and from viewer to viewer. Therefore:
- When shopping for a lens with bokeh in mind, make sure to look at example shots or shoot with the lens yourself. Don't trust others' reviews if you can't see what the resulting images look like.
- Don't freak out if someone else doesn't like the bokeh in a shot you like. It's a matter of taste, for which there is, famously, no accounting.
What impacts bokeh
There are a number of factors which determine how a lens will render out of focus areas. Some of these are simpler to understand than others.
The shape of the aperture will determine the shape of OOF highlights. (The round or polygonal shapes that appear when a specular highlight is out of focus.) If the lens is wide open, this will be a circle. If the lens is stopped down, the OOF highlight will take the shape of the aperture. The more blades in the aperture, the rounder the shape will generally become, and the fewer blades, the more polygonal and chunky the shape will become. If a rounder OOF highlight is desirable, a lens with more aperture blades is a good idea.
The aperture shape also influences the overall smoothness of OOF areas. A rounder aperture will yield smoother OOF areas, all else being equal. For many, this is a desirable characteristic.
There are a number of other factors which are somewhat more difficult to explain, such as spherical aberration, chromatic aberration, etc. Until someone smarter than me comes along to expand on these things, please consult the Links.
Bokeh and Flickr, HBW!
Every Wednesday there is a phenomenon that hits flickr: HBW. HBW stands for "Happy Bokeh Wednesday" where users post bokeh shots, adding them to the Bokeh Wednesday groups. Users on these groups post photos and comment heavily on other images in the pool replying with HBW. It's a pretty large movement which actually changes flickr explorer. Explorer on this day will be flooded with Bokeh Wednesday shots.