Ah, point taken - but I still think the difference is only enough to
push
"almost ugly" bokeh to "ugly bokeh". I have never seen any amount of
USM or
contrast pushing turn truly smooth, pleasing bokeh into harsh, ugly
bokeh.
Similarly, strong USM introducing stair-stepping is not something I
have seen
in anything better than an 8-bit-per-channel file, and certainly never
with
film!
I have also found symmetrical large-format lenses to have beautiful
bokeh.
I am no expert, but I do use a Schneider Super-Angulon 90mm f/5.6 XL
quite
regularly, and even when stopped down, the background blur is
beautiful, it
sucks your eyes in...
keep well!
Dawid
On 03 Dec 2008, at 7:08 PM, Ken Norton wrote:
> When you apply USM (unsharp mask) to an image that contains
> gradients, what
> can happen is the change from a smooth gradient to a stair-step.
>
> Depending on the lens design, focal-length, and aperture, the bokeh
> of an
> out-of-focus highlight will look like an balloon with a soft edge.
> Depending on these three factors, the transition between what I will
> refer
> to the "umbra" (solid balloon) to the "penumbra" (the fade-zone) is
> what
> makes or breaks the bokeh.
>
> Some combinations will yield a wide penumbra, whereas others have
> nearly no
> penumbra. Sometimes, you will encounter a lens-aperture combination
> where
> the penumbra wraps back onto itself and you'll get a bright rim
> around the
> balloon. This is very common with wide-angle lenses with asymmetric
> lens
> elements where they induce astigmatism when shot wide-open. In some
> extreme
> cases, with wide-angle zooms, you'll actually get donuts.
>
> A lens, which is "symmetrical" in design, such as those typically
> used on
> large-format cameras will usually have have the penumbra starting
> immediately from the center of the OOF (out of focus) highlight) and
> will
> have a relatively smooth roll-off all the way out.
>
> If you apply a bit too much USM to a photo, a lens which produces a
> narrow
> penumbra will show a relatively smooth, but short transition without
> USM,
> but will "donut" with USM. Backing off USM from "donut mode" will
> create a
> harsh step and essentially eliminate the penumbra.
>
> AG
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