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Originally Posted by
rpcrowe
Now for BOKEH. Bokeh is a Japanese term for the subjective appearance of the areas which are out of focus.
The differences in bokeh are caused by the shape of the lens aperture, a lens such as the Canon 50mm f/1.8 Mark-II has only five aperture blades and thus the shape of the aperture is not a clean round hole. It is somewhat ragged since five blades cannot make a clean circle.. A lens such as my 90mm Tamron f/2.8 Macro has nine blades and those nine blades can form into a cleaner and more even circle as they are stopped down. The out of focus areas from my Tamron are more pleasing in looks than the out of focus areas from the 50mm f/1.8 lens. The bokeh formed by the 50mm is often described as "ragged" while the bokeh formed by the Tamron is often described as "smooth and creamy".
Smooth bokeh is not distracting to me (see, I told you this was subjective) while ragged bokeh can tend to be distracting. We often use depth of field in order to accentuate the interest on our main subject but, when the OOF areas compete for that interest, the attempt fails somewhat. IMO, bokeh is particularly important in portraiture and in macro photography.