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| Photo by Yassine Hakimi |
What is Bokeh
You probably already know that your camera lens can focus sharply only at one distance at a time. Bokeh (derived from Japanese, which means "blur" or "haze") refers to the visually distinctive look of sunshine within the out-of-focus areas of a photograph In a zoom lens, for example, each focal length can focus at a specific distance. Every other distance--closer or farther--blurry will appears.That blur is caused when the sunlight that bounce off objects in the scene and pass through the camera lens don't all line up properly on the image sensor. And as these light rays pass through the lens, they diffract around the lens aperture, causing each "blurry" point of light in the image to take on the distinctive shape of the aperture itself.
Lets take a look for some examples? this shoot that have a bunch of lights and reflections within the background, that makes this image an excellent playground for investigating bokeh. The following details show some of those reflections.
First shot, notice the roundness of the blurry part, which may happen when the aperture is totally open, so the barrel of the lens (not the aperture) determines the shape of the bokeh.
Here's what the a similar scene would appear like using a relatively cheap lens that contains a five-blade aperture. Notice how the blue takes on an angular character.
Now contrast that with the same setup, only using a lens with a nine-blade aperture. The blur is more soft--almost as round as the first photo.
Here's a wierd one. This image shows donut-shaped bokeh--hollow circles. This is what you get when you use a catadioptric lens. The circles are hollow as a result catadioptric lenses use a telescope-like mirror and a small second mirror to replicate the image onto the sensor, and that mirror blocks the light from the larger primary mirror.
What is good bokeh?
As the examples above, perhaps we will answer the question: What is good bokeh?Well, as in any creative endeavor, it's subjective. however in general, photographers tend to like smoother, rounder bokeh--the kind you get from lenses with more aperture blades. It's no surprise, then, that high-quality short telephoto lenses (the kind favored by photographers for portraiture) usually feature nine-blade aperture blades, which yield very round bokeh.
While everyone is entitled to their opinion, I doubt you'll find many photographers who like the bokeh you get from a catadioptric lens. Not only are those donut-shaped blurs ugly, but they are too sharply defined. And that's another aesthetic consideration--is the blur distracting? The more sharply defined the edges of the blurry elements, the more distracting the blur will be in the photo. Blur should never steal your attention.
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