Expand Your Word Power: "Bokeh"
I have no idea how it’s supposed to be pronounced, but I learned a new word today.
“Bokeh” is the term used to describe the blur that occurs in the out-of-focus areas of a photograph outside the image’s depth-of-field range. More specifically, it describes the aesthetic qualities of the blur.
A “good” bokeh is generally a smooth and soft blurriness, without jagged edges on highlights that distract from the photograph’s subject. Better bokeh can result from having many blades on the lens aperture, as the resulting aperture has smoother, more rounded edges than an equivalent lens with fewer blades on the aperture. The Canon EF 50mm f/1.8 Mark II lens has only 5 blades: its out of focus highlights tend to resemble pentagons, and out of focus areas have a rougher texture that distracts from the subject. My Canon EF 50mm f/1.4 lens has 9 blades, and its out of focus highlights resemble smooth circles, with better bokeh lacking as many distracting artifacts. Here’s a comparison of the two – the f/1.8 on the left, the f/1.4 on the right:
For a more extensive comparison, check out this page (the source of both images above) which has plenty of images that show the difference in results between the lenses: http://photo.net/equipment/canon/ef50/.