Having used (or attempted to use) selective DOF much more recently, the
nature of the background and lens opening used can also affect how
pleasantly out of focus regions of the image are blurred. A background
softly lit with diffused light is much more forgiving. Harsh, brightly lit
backgrounds with distinctly defined pinpoint highlights (far enough apart
they do not blur together) are a real test. If out of focus, these
pinpoints of light will tend to pick up the shape of the aperture; the
harsher, brighter and more pinpointed, the more the effect. I have found
with the 28mm f/3.5 that it has reasonable bokeh wide open with a circular
aperture. Stopped down to between f/8 and f/16 gives a definite hexagonal
aperture that can easily be picked up by out of focus pinpoint highlights.
Don't confuse this with off-axis flare from something like the sun which
can also pick up the aperture shape as the light bounces around off the
inside of the lens barrel and the air-glass surfaces.
OTOH at night with available light, stopping down some can give a pleasing
(to some at least) diffraction flare from ambient incandescent (or other
point source) lights caused by the thin blade edges in a star shape, the
number of points of which will match the number of aperture blades. This
isn't bokeh but yet another aspect of lens personality.
My conclusion is how a particular lens design behaves depends on how one
uses it and the lighting conditions under which it is used. Sometimes you
might not *want* that super-speed lens if using an f/3.5 prime wide open to
a round aperture instead can produce the softer image with good bokeh.
Really knowing one's lenses can pay off with lens selection criteria for a
task being more than just a focal length.
-- John
At 16:33 3/18/00 , Giles wrote:
>
>It is mentioned when describing a lens because not all lenses blur the
>background, or foreground, in the same way. There can be a sort of
>flavour to the way things are blured. Some lenses have a very pleasant
>smooth sort of bokeh whereas others can give a distracting and harsh
>appearance to blurred areas.
>
>A lens with pleasant bokeh is often very good as a portrait lens as the
>smooth blur somehow seems to make the in-focus subject stand out and seem
>3D.
>
>Giles
>
>John A. Prosper wrote:
>
>> |I hate to expose my ignorance to the whole world, but what does "bokeh"
>> |mean?
>> It's a Japanese term which means "pleasingly out of focus"; in other
>> words, pleasant background blur---as in portraits.
>>
>
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