In photography, bokeh (pronounced /boʊ'kɛ/) is the blur, or the aesthetic quality of the blur, in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light." Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—"good" and "bad" bokeh, respectively. Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.
Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas. However, bokeh is not limited to highlights, as blur occurs in all out-of-focus regions of the image.
The term comes from the Japanese word boke (暈け or ボケ), which means "blur" or "haze", or boke-aji (ボケ味), the "blur quality". The Japanese term boke is also used in the sense of a mental haze or senility.
The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the March/April 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying "it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable". Bokeh replaced the previous spelling boke that had been in use at least since 1996, when Merklinger had also suggested "or Bokeh if you prefer."
The term bokeh has appeared in photography books at least since 1998. It is sometimes pronounced /ˈboʊkə/ (boke-uh).
With large aperture, you'll get a great bokeh
The depth of field (DOF) is the portion of a scene that appears acceptably sharp in the image
50mm will give you a great portrait pictures