Let's Cut the Bokeh...

[Jason Greenberg Motamedi]

When I first read the word "bokeh" I thought the writer had misspelt "bouquet". To this day, I continue to think of the bokeh of a lens like the bouquet of a wine--I am fascinated by it, but don't really understand it. Beyond this, the language and vocabulary which is often used to discuss both bokeh and bouquet tend to obfuscate (!) the subject, making entry difficult for laypeople.

That said, there are clear differences between the ways that older lenses, particularly portrait lenses, render out-of-focus space. There seems to be a relationship between optical "correctness" and bokeh. To a limited extent, the poorer the corrections, the "better" the bokeh. The examples above, the Verito and Heliar, are certainly less perfectly "corrected" than a modern Plasmat, and their bokeh is both identifiably different and often judged more attractive. Petzval type lenses, which were used in the 19th and early 20th century for portraiture have a very easily identifiable "swirly" bokeh, which looks unlike any other and makes the f/64 crowd cringe.

For the record, "bokeru", not "bokeh", means senile.

[David du Busc]

I believe we've entered the circle of confusion.... so let's talk about that too.
Tally Ho!

[paulr]

one thing to remember: since bokeh has to do with areas that are out of focus, it will make little difference to you if your style of photography involves using movements and small apertures to bring everything as close to in focus as possible.

i don't usually have a lot of visibly unfocussed things in my pictures, so naturally i tend to care more about how the lens makes the focussed parts look. but this is really just about stylistic choices.

i read an excellent article about bokeh, which attributed much of what the bokeh fetishists talk about to the way spherical aberation is corrected. the article (which i'd link if i could remember where it was) showed different examples of out of focus points of light against a dark background. in all cases, as you'd imagine, the point becomes a circle as it's defocussed. but the character of that circle is different from lens to lens. in a lens that has "perfectly" corrected spherical aberation, the circle is uniformly shaded and has a smooth border against the background. this is, of course, perfect as defined by modern optical engineers. the bokeh people consider this to be only ok, in general. in the lenses with slightly undercorrected spherical aberation, the point was brightest in the middle and faded gently into the background. most of the bokeh people like this the best. in a lens with overcorrected spherical aberation, the effect is the oposite, and actually looks like a circle of light with unsharp masking applied: it has a bright halo and an abrupt transition to the dark background. few people like this effect.

here's the catch: if a lens has undercorrected spherical aberation (and smooth transitions from light to dark) in areas that are farther than the focal plane, it will tend to have overcorrected spherical aberation (and abrupt, ugly bokeh) in areas that nearer than the focal plane. and vice versa. so it's unlikely that you'll have a lens that looks great both in areas that farther and closer than the focal plane. this may be a reason people have different lens preferences: anyone who tends to defocus the foreground will like a different set of lenses than someone who tends to defocus the background.

[David A. Goldfarb]

In the case of Petzval lenses (I just acquired one myself) the swirly look is also coming from the very visible curvature of field associated with Petzvals. Since they were designed as fast portrait lenses (f:3.6 or thereabouts), sharp corners could be sacrificed for speed.

[Oren Grad]

Emmanuel - Thanks for sharing that fascinating post from the Rollei board. I did a bit of homework with my Japanese dictionaries, and discovered that the same character (kanji) is used for both "bokasu" and "bokeru" - that is, it's used to express both the concept of tonal gradation, and the concept of blur or being out of focus.
That's pretty remarkable, I think. Although they are different concepts, together they go much of the way toward capturing what's distinctive about the character of a lens. In current usage in the Japanese photo magazines, sometimes bokeh is used to refer strictly to the character of the OOF blur, but sometimes to refer to the optical character overall, including the smoothness of tonal gradation.

Jason - Although they are homonyms, the kanji used for bokeru "senile" is different from the one used for bokeru "blur" / bokasu "shade off", though there may some overlap in actual usage.

Paul - From your account, the article you're referring to is probably Harold's - see link above. Your reminder about the tradeoff between background bokeh and foreground bokeh is a good point. Regulars here may remember that I'm a big fan of the Apo-Sironar-N and-S lenses, which to my eye have exquisite background bokeh. But the foreground bokeh, while generally tolerable, is in many situations not nearly so pretty. There are a few lenses that manage to get around this, though - Mandler's 35 Summicron-M (the last pre-ASPH version), for example, trades off other forms of correction to deliver bokeh that's pretty well controlled in both foregrounds and backgrounds. I woudn't be surprised if there are some older LF lenses that achieve the same. David - what's the Heliar like in this respect?

[David A. Goldfarb]

The Heliar is pretty well controlled in front and in back, but I tend to put more background out of focus than foreground, and my instinct is that it's smoother in back than in front. I couldn't find a handy LF Heliar shot that I've scanned with OOF areas in front and in back, but this is close--a shot on 35mm with a converted 100/3.5 Medalist Ektar, which is a coated Heliar type:





and it's pretty sharp in the sharp area for a handheld shot--

[Bill Smith]

I think the literal translation of boke is "blur".
This whole subject is boring.

[paulr]

Thanks for the clarity, Bill. for a minute there I thought it was interesting.

[tim atherton]

"I think the literal translation of boke is "blur". This whole subject is boring."

quite possibly almost as boring as "what movements do you use on a technika" or "what dos Angulon mean"....

[Scott Rosenberg]

but not so boring as to keep you from reading the thread and posting a reply. i really wonder about the folks on the forum that spend their time replying to threads without actually contributing to the exchange of information therein. just practicing your typing i suppose? why not simply send yourself emails - at least then you're only wasting your own time.

for those of you that actually posted with useful information, i appreciate it very much - the links were very informative. those, along with some others i came across, have really cleared up the whole bokeh thing for me. it’s actually quite a fascinating study, at least I think so, and looking into it has really taught me some new things about optics and the developments made over the last century.

again, thanks for the education,
scott