Bokeh:
While many concern themselves with what *is* in focus, bokeh is about what
is *not* in focus. As important as contrast and resolving power is to a
lens, its "bokeh" or how it handles what is out of focus is important also
if you make use of a shallow "Depth of Field" for slectively focusing on
your subject.
Theoretical aspects of focus and what can go wrong:
An out of focus point of light is theoretically a "circle of confusion."
That is, it turns into a fuzzy circle. The more out of focus, the bigger
the circle. Think of two cones, point-to-point. When the point is in
exact focus, the film plane is where the two light cones meet and you get a
point on the film. Focused in front or behind the light point, you get a
circle with fuzzy edges and reduced contrast.
No lens is perfect, and its "bokeh" can be different with points of light
closer and farther the exact focus distance. One of the imperfections can
be "coma" where the fuzzy circle has a small tail on it like the
punctuation mark it is named after. A good lens design (and a lens in good
condition) will not have "coma." Another is the circle taking on the shape
of the aperture blades. The f/1.4 and f/1.2 50mm Zuikos (along with a few
other of the faster [more expensive] primes) have eight blades. The f/1.8
50mm and most of the primes have six blades. If, instead of a fuzzy circle
you see a fuzzy hexagon or octagon, this is what has happened. Yet another
is not having a soft fuzzy edge to the "circle of confusion", but a sharp
harsh one.
All these things (and perhaps more) contribute to a lens' "bokeh." Bokeh
is more generally more important with a long telephoto than it is with a
super wide-angle, as you will likely encounter portions of your image out
of focus more often with a long telephoto than with a super wide-angle. It
is also important with macro work which often has very shallow depth of
field. These are generalizations. If you do any photography which has
portions of the image out of focus, knowing the bokeh of your lenses (wide
open versus stopped down, in front of versus behind the focus distance,
etc.) can help you create a better image in composing it beginning with
lens selection (if you have a choice).
-- John
At 02:19 6/19/00 , Wayne wrote:
>Am relatively new to the list, and recently back to my OMs (3 plus 10
>lenses) after leaving them on the shelf for about fifteen years. They
>still work great - its me who is a little rusty.
>
>Saw "Spiratone" listed in a post. What ever happened to them? Did they
>become another company or just fade away. Aside from a lot of low cost
>"juncque" they had a few nifty tools and accessories for close up work.
>
>And, please, what he heck is the specific definition and origin of
>"bokeh" I have surmised the general meaning, but am still curious.
>
>Thanks,
>
>Wayne
>
>
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