Bird bokeh

Was listening to a tutorial/review that discussed the topic of bokeh last night.

Turns out a handy way to measure "blur quality" is to divide a the lens' focal length by the f-stop. For example, Canon's 85mm f1.8 lens churns out a spectacular 47 bokeh-blur (BB) score. Since I don't have an 85 mm lens, I settled for my 55-250 IS during my afternoon walk.

Surprisingly, the "kit zoom" produces some respectable bokeh-blur numbers on paper. At 85mm, the widest it can get is a mere f4, yet that offers a passable 21 BB. When you crank that puppy up to 250mm at f5.6, however, the BB soars to 44.6.

A few test shots at 85 and 250 mm were enough to reveal a significant difference in the blur factor — think chunky vs. creamy smooth peanut butter. Sure, shooting at 250mm can put you in the middle of the road or make you feel like a stalker, but it's all about the blur.

In the end, I ended up grabbing a shot of some quail that have taken up residence in a tree near my office. Shot this image at 215mm with an f6.3, so the BB comes in at about 34.