[Leica] bokeh

["Jonathan Borden" <jborden@mediaone.net>]

Mike Johnston
>
> Regardless of what you think personally, there is no correllation
> between conventional "optical quality" and successful expressive
> photography; it's easier to find examples of negative correllation. So
> we have to realize that the basic predicates of most "lens testing" may
> in fact be useless to certain individuals vis-a-vis their needs.

The pictoral school of photography has been around for a century. I imagine
that the "Diana" branch would shun all things Leica. We should remember that
even the old uncoated lenses which we now consider optically inferior were
terrific lenses in their time. To me there is a difference between using a
lens that was great in its day, though may exhibit a greater degree of
optical aberration than in a modern lens, vs. seeking out a crappy lens to
prove a point. To each his or her own.

>
> Incidentally, "bokeh" qualities can be measured; it just isn't done in
> conventional lens tests.

What are the "bokeh" qualities (stress plural). The terms I read are "harsh"
vs. "smooth", is there a set of qualities?

The point spread function of a lens describes the out of focus information
precisely. I suspect that if you can develop a language to describe "bokeh"
properties, this will highly correlate with the shape of the lens' PSF. Are
you aware of lens designers who try to optimize "bokeh" in specific, or
rather is this a side-effect of attempts to minimize aberrations.

Jonathan Borden