[Leica] Test for Bokeh

[Mike Johnston <michaeljohnston@ameritech.net>]

By the way, it's very easy to set up a standardized test* for bokeh,
assuming your investigations are directed at your own education and not at
some pretense at science.

Lenses tend to render worse bokeh a.) with the focus distance set close, b.)
at wider apertures, and c.) with high contrast objects (subject matter) in
the background, far from the pobf (plane of best focus).

So, simply find a situation that you can set up repeatedly that satisfies
these conditions to some extent, make pictures, and look at them. You'll be
surprised how mch you can learn about your lenses.

I'd recommend being moderate rather than extreme in your demands for all
these conditions. For instance, my "test" was to set up a tripod in my loft
and focus the lens on a book about six feet from the camera, which I placed
in the lower right-hand corner of the frame. There was complex object
information (a big wicker chair, usually with my kid on it watching TV)
about 15 feet from camera position, high contrast subject matter (a stair
railing, sidelit by a big window) about 30 feet from camera position, and a
dark office platform with lamps on the desk about 40 feet away. I'd simply
make photographs at all apertures and look at them.

I'd usually augment this with a "stress test," which was simply my glasses
on my desk shot wide open with the camera as close as I could get. I'd
arrange it so there was a brick wall about 3x minimum-focus-distance away
and then look at how each lens rendered the brick wall.

It's really not difficult to see major differences in the way lenses behave.
Bokeh is quite easy to see, and (even within the same line of lenses)
differences between various lenses can be quite pronounced.

Among other things, you will learn 1.) which of your lenses give the best
bokeh at or near wide open, and 2.) at what aperture each of your lenses
"cleans up" in terms of bokeh (most lenses are rendering acceptably smooth,
non-distracting bokeh by f/5.6). For instance, if you perform this test with
the 50mm Summilux-R (55) and the 50mm DR Summicron-M, you will see major
differences in the way these the bokeh of these lenses behaves at their
widest apertures.

As far as what bokeh you _like_, or is best, no, there is no test for
that--with some things in photography, like it or no, you just have to look
at pictures and let your personal taste be your guide.

- --Mike


* bear in mind that virtually all "tests" in photography are really just
trials. But that's okay, since all that most of us want to do anyway is try
things to see how they work for us. Your goal in all of this should simply
be to learn the way your lenses behave, so that (if you prefer to) you can
accomodate their weaknesses and play to their strengths when you're
shooting, and not find yourself unpleasantly surprised by results you didn't
anticipate. (This is also a goal of learning about other aspects of
photographic technique.)