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[OM] Re: [Way OT] Allison on the north shore was;...

Subject: [OM] Re: [Way OT] Allison on the north shore was;...
From: AG Schnozz <agschnozz@xxxxxxxxx>
Date: Tue, 23 May 2006 21:49:33 -0700 (PDT)
> mind translating for the slow-brained types? "cold in the
> Bokeh" means? should be lower F-stop or just bad lens design?

LOL! You like my new coined term?

Let me describe by example:  A prime lens that is symmetrical in
design will tend to allow the bokeh to "bloom" at a linear rate
the farther from the plane of focus the OOF highlight is. Not
only that, but the edge of the highlight continues to soften.
Changing apertures doesn't change the nature of "bokeh
expansion", just the rate.

Modern zoom lenses almost always have a limited "bokeh
expansion". The farther the OOF highight is from the plane of
focus the less the growth--eventually reaching a point where no
further expansion occurs. When this happens, the OOF highlights
will tend to resemble bubbles with a well-defined outer-edge.  I
believe this is due to the aspherical lens elements as well as
the non-symmetrical nature of nearly all focal lengths the zoom
lens covers.

You might ask what this has to do with "warmth" of the image.
Maybe warmth is the wrong term to use, but I believe that this
progressive bokeh expansion of some classic lenses helps the
focused-upon subject to seperate from the background better.

Focal-length, aperture and subject distance to background ratio
all are major factors in determining bokeh.  Even blade shape.
But lenses that freely allow the "bokeh bubbles" (another coined
term) to expand freely will give a softer, smoother background.

Back to "warmth". I believe where I'm going with this is a
rather radical concept:  We all know that an OOF highlight will
bleed into the surrounding shadow area. But I also believe that
the OOF shadow will bleed into the highlights. My 100/2.8 with
about 25mm of extension (1:4 magnification) will lose almost 1/2
a stop in a background that is greater than 2x the focused
distance. This is above and beyond the normal loss due to
extension. The "light falloff" further helps bring the subject
out from the background. Depending on the nature of the film or
sensor, this under-exposureness may trend towards an actual
warming of the scene.

I definitely wouldn't call a modern lens "flawed" or "bad".
They're more accurate and sharper than anything that fits one of
my OMs. Furthermore, I believe the aspherical lens elements
create a thicker plane of focus.  Instead of perfect focus being
a plane that intersects the scene, it actually has some depth
with the modern lenses. At any given aperture, my DZ 14-54 tends
to have more in focus than my 50/3.5 or 35/2.8.

AG

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