Let's Cut the Bokeh...

[Scott Rosenberg]

allright, i've been doing a lot of reading, a little thinking, and some head scratching. a recent thread on the view camera forum got me thinking about the whole concept of bokeh, which i've heard translated to bull$hit or senile. regardless, i'd like to hear what your theories are as to the factors that create this nebulous quality in the oof areas.

i'll mention the theories i've come across thus far...
1. the number of blades in the iris of the older shutters create a softer image in the oof areas.
i've come across this one several times, but then what of all the old lenses that have been moved into modern shutters? would this not make all lenses in, say copal shutters, identical in this regard?

2. before lenses were APO corrected, the red, green, and blue light all came into sharp focus at slightly different points, creating a tunnel of sharp focus, rather than a discrete point of sharp focus.
i can accept this in theory, but do not know enough about optics to form a real opinion on this one.

any other theories? could it just be a characteristic of the glass... just like the contrast, sharpness, or color cast is a characteristic of a particular lens?

any thoughts, theories, or ideas on this? i think it's high time we cut the bokeh and get to the bottom of this!

scott

[David A. Goldfarb]

The shape of the stop determines the shape of out of focus highlights, and round ones look a little less unnatural than pentagonal ones, I suppose, because the eye has a fairly round stop, but I don't really think this is a major factor that affects the overall look of out of focus areas (except in the case of mirror lenses that have a ring-shaped stop).

Usually overcorrected spherical aberration is cited as a cause for "bad bokeh," which manifests itself in various forms, like double-lines in out-of-focus areas or out of focus highlights that are brighter at the edges than they are at the center.

With some lenses, like the Verito, uncorrected chromatic aberration takes some of the edge off even when the lens is stopped down sufficiently to reduce the effect of uncorrected spherical aberration. Chromatic aberration may not have been so visible, though, in the days of orthochromatic films, and it can be corrected by using a strong monochromatic filter with B&W film.

It's only recently that the quality of the out of focus image has been called "bokeh," but if you read historical materials about soft focus lenses, all these issues are mentioned. They're just called "distracting double lines" and "cluttered backgrounds."

[Jim Galli]

"i think it's high time we cut the bokeh and get to the bottom of this!"

Scott, It's a bottomless pit. You've entered into the shifting sands of subjective opine here and there are no rules. No science. Just trial and error. And lots of opinions.

[Oren Grad]

The number of blades in the iris has some effect on the bokeh, but it's not anywhere near the whole story. The four major modern lens lines - Rodenstock, Schneider, Nikon and Fuji - all look different in the OOF areas, even though they use identical Copal shutters.

Bokeh is determined by the sum total of the optical design - which is to say, the combination of glass types, the number and surface curvature of the lens elements, and their grouping and spacing relative to each other. The handling of spherical aberration is certainly an important part, but tradeoffs in correction of other aberrations matter as well.

I don't think anyone has published a rigorous and exhaustive account of the optical design factors that determine bokeh, at least not in English. But if you haven't already done so, you should read the article by Harold Merklinger that appeared in the special bokeh feature that appeared in Photo Techniques magazine back in 1997:

http://www.trenholm.org/hmmerk/ATVB.pdf

David is mostly right about the relatively recent emergence of the term "bokeh". That's true for its widespread use in English, which I suspect can largely be traced to the PT feature. The Japanese usage, however, goes much further back. There's probably an interesting historical tale to be told about its true origins, waiting to be uncovered by someone who can read the Japanese literature going back many decades.

[Alan Davenport]

... the view camera forum got me thinking about the whole concept of bokeh, which i've heard translated to bull$hit or senile.

Good luck with this question. Most of the threads I've ever seen on "bokeh," ultimately translated to one or the other.

[Peter Galea]

Doesn't this belong in the Leica Forum?

[Oren Grad]

I have to disagree a bit with Jim.

There is science, even if it's not complete - just read Harold's article for some excellent science that goes a long way toward demystifying the effect, even if it doesn't account for all of the subtleties.

Selecting a lens with pleasing (for you) bokeh is also more than just trial and error, but as with other aspects of selecting equipment, you do need a bit of experience under your belt in order to have a language to describe it. It is, of course, exceedingly difficult to directly characterize the "look" of a lens is an unambiguous way - one ends up using vague adjectives that don't communicate well to someone who doesn't already know what you're talking about, and which understandably elicit a fair degree of skepticism. But once you know the "signature" of various lens types, it's not hard to characterize a newly-encountered lens by analogy to known types. If someone who pays a lot of attention to these things tells me that a lens looks, say, more like a Fujinon-W than an Apo-Sironar-N, or more like a coated Goerz American Dagor than an Apo-Symmar, I know *exactly* what he's talking about, even if it's hard to put into words.

If this sounds strange, remember that the same is true of many other everyday characteristics that we take for granted. For example, try describing a new flavor without drawing analogies to foods that you and your audience have both already tasted. Food scientists have a language for the elements that go into a given flavor that can tell part of the story, but for the rest of us, a well-drawn analogy is pretty much the only way we have to communicate what we mean.

[Emmanuel BIGLER]

There's probably an interesting historical tale to be told about its true origins, waiting to be uncovered by someone who can read the Japanese literature going back many decades.



At least some information about the origins of the word 'bokeh' has been presented here on the RUG in January 2004 by Todd Belcher



"Bokeh : The shape of the out of focus area of a photo." (Peter Kotsinadelis)



Then, Todd Belcher argues and explains the Japanese origin for this word:
(RUG, January 2004) http://digistar.com/rollei/2004-01/2521.html http://digistar.com/rollei/2004-01/2532.html



"I don't think that's the definition of Bokeh, Peter. Though that is
definitely an aspect of Bokeh. I think a definition of Bokeh would be
more along the lines of: the ability of a lens to render gradations. It
is considered good Bokeh when the gradations are smooth and poor Bokeh
when the gradations are harsh to the eye. The Harshness can be caused
by, as you say, out of round apertures, but can also be caused by the
lens itself. Symptoms of the latter are hard gradations and double
image out of focus areas.
Bokeh was coined by the Japanese and comes from the Japanese word for
gradation: 'bokashi'. The Japanese have, for many centuries, been
concerned with gradations in art, thus, it was not a big step to
consider it's implications in photography....
...
It is indeed related to Ukioye, Japanese woodblock printing, where
gradations were difficult to produce. The pressing of each sheet to
the woodblock had to have the ink wiped on to the woodblock 'just so'
to attain a nice gradation. In some areas, such as the face of a
character, very small areas may have had gradations and these required
a highly skilled printer to apply with consistency. The Japanese
prized the skill with which these gradations were made and effect they
had on the final image. these gradations made an appearance in
Japanese woodblock prints towards the end of the 1700s and early
1800s. --Todd Belcher"

[Ole Tjugen]

"Trotz scharfer Zeichnung bei hervorragendem Auflösungsvermögen hat das Heliar keine kalte und harte, sondern eine duftige Schärfe, die den Übergang von der schafen zur unscharfen Zone mildert, die keinen Bildteil unangenehm hart hervortreten lässt, sondern dem ganzen Bild eine harmonische natürliche Abrundung gibt."

> Despite sharp results with outstanding resolving power the Heliar does not have cold and hard, but a fluffy sharpness, which moderates the transition from the sharp to the indistinct zone, so that no picture part will stand out as unpleasantly hard, but gives a harmonious natural rounding to the whole picture. <

Advertisment for Voigtländer's Heliar lens in "der Satrap", March 1933.

Good Bokeh is nothing new, and lenses have been designed with that in mind for a long time. Only the word is recent.

[Steve Hamley]

Anyone that doesn't believe in bokeh contact me off line and I'll buy those lousy defective Heliars of yours at 1/4 the going price....

Seriously though, I do agree with Jim, not because bokeh can't be defined or illustrated, but because "bad" bokeh bothers different people to different degrees - some not at all and others it drives nuts. I tend to fall in the latter camp; looking at a picture with truly bad bokeh makes me think my eyes are crossed.

But there's another argument that "not so bad" bokeh with the beginnings of the double image acts like an unsharp mask in Photoshop creating an appearance of sharpness. Maybe, maybe not, but an interesting thought.

Steve