Bokeh, was Re: Direct negatives from slides

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From: Sandy King (sanking@hubcap.clemson.edu)
Date: 03/28/01-11:31:58 AM Z


Carl,

Yes, I remember making that comment about the print from the 16 1/2" Dagor,
though I don't recall that you explained the effect as the result of bokeh.
So what is bokeh caused by, some kind of combination of lens aberrations
that makes the transition from in-to-out of focus smoother.

Sandy King

>
>Actually, you spontaneously commented on the excellent bokeh displayed by my
>16.5 inch A.O. dagor when looking at the picture of the overpass with sumac
>in the shadowed foreground. You noticed that the f/g looked wonderful even
>though it couldn't possibly be in focus: that's a perfect example of a lens
>with favorable bokeh characteristics. The smoothness of transition from
>in-focus to out effectively extends the depth of field.

Lenses with really
>awful out of focus character show a sudden, harsh transition. With strong
>selective focus, the blurred areas can look almost as weird as the
>donut-shapes you get with a mirror lens. In one example I saw, there was a
>liquor bottle in the background. In the lens with unfortunate bokeh, you
>could more or less tell it was a bottle. In the lens with beautiful bokeh,
>you could tell what brand it was because the logo, though blurred, was
>recognisable even though technical depth field was of course the same. Wish
>I remember where I saw that pairing.
>
>The first time I encountered the concept stated as such had nothing to do
>with Japan: Bill Pierce about ten years ago told me about a conversation
>he'd had, ten years earlier still, with the Leitz designer responsible for
>the Noctilux. What he said was simply that at f/1, invariably most of the
>picture will not be in the plane of good focus. So it makes sense to pay
>attention to the look of the out-of-focus image when designing the lens. In
>fact, I'd been aware of the difference on a gut level since the 1970's when
>I began using Leitz lenses for all my personal work even though I had a
>complete set of Nikons for commercial assignments. Art directors were happy
>with chromes from the Nikkor glass, but my b&w prints from Letiz lenses were
>invariably more pleasing, and this smoothness of focus transition is a vital
>element of the difference. But most of this work was in low light with
>lenses near wide-open. Most commercial work had artificial lighting and deep
>focus.
>
>With a 6x9cm stopped down to f/32, there won't really be any out of focus
>stuff unless your subject is quite close, within 4 or 5 feet I'd guess.
>
>---Carl


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