bmike101 Loc: Gainesville, Florida

I have two lenses: a nikkor 18-55mm f3.5 and a nikkor 55-200mm f5.6 (both kit lenses). The problem (not really a problem) I am having is that with the 18-55mm getting bokeh is difficult unless you are zoomed all the way in whereas with the 55-200 it is hard to get rid of. Is this normal? Why is it this way (meaning why does bokeh happen more with the 55-200? I remember hearing that bokeh has to do with the aperture and the f# determines that. Is that why it works like that?
I am soon getting a sony (if all goes according to plan) and the lenses will be a 16-35 f2.8 GM and a 24-70 f2.8 GM . Will these two lenses behave the same way? I wouldn't think so if the aperture theory is correct.... but what do I know after all!

GalaxyCat Loc: Boston, MA

What is "bokeh?"

RichardTaylor Loc: Sydney, Australia

It is the quality of out of focus backgrounds - good lenses give you very smooth backgrounds.

Rongnongno Loc: FL

Bokeh is prevalent in long lenses and sometime existent in wide angle. The aperture plays a minor role but does influence the final result.

Why? 'Perspective compression'. Look it up.

the 16~35 will produce very little bokeh.
The 24~70 will produce more in the range above 50mm.

Rongnongno Loc: FL

Charles 46277 Loc: Fulton County, KY

Bokeh and depth of field are two different concepts. Any lens only focuses on one plane, a thin flat field, but depending on the size of the aperture, the areas in front of and behind this thin plane will look more or less sharp. In olden times, the longish lenses used for portraits had large apertures because they used the existing light, but this made a very thin depth of field--the eyes were sharp, but the nose and ears--not so much. Since this effect was common with the great portraits of old, everybody tried to duplicate it, even though we had enough light for smaller apertures and good sharpness throughout. So that is the style issue, of expecting backgrounds (especially for people) to be out of focus.

Recently (a few years--not decades) ago, the Japanese applied their word, "bokeh" to describe a certain preferred look for the out of focus background (foreground too, if appropriate)--not all lenses gave the same look, even at the same settings and distances (and focal length). The word "bokeh" is not a scientific or descriptive term in any strict sense--it is an artistic interpretation, and so as far as I know, it is the result of one scientific factor--the shape and thickness of the aperture blades when the exposure is taken. Old lenses uses so many blades that the circle was nearly a perfect circle, without noticeable corners between them; but by the 1950's, even large format lenses were using apertures with only 5 blades, making a hole the shape of a pentaprism; or sometimes a few blades more. This had no noticeable effect unless you shot into the light--in that case, the point of light took on the aperture shape, so you got pentaprisms or other patterns of light within the photo, where the light was or reflected to other places by each of the elements of glass in the lens. Some people like this, but most people consider it something to avoid--coated lenses helped a lot, and the use of a shade or hood around the lens also helped.

But more recently (I don't know just when), the above mentioned Japanese saw that even in good light (above and behind the photograher, for instance) there was a different sort of look, or quality, to out-of-focus backgrounds when the lens was set to larger apertures (or anything that is well outside the place of good focus), which was related to how many blades were in the aperture. Round apertures of old, they said, looked better in the out of focus areas--they rendered a better "bokeh." What is better or worse in this regard is not a scientific question, and even in regard to artistic states, it is not entirely clear what people mean by good bokeh--maybe, today, many people just mean the bokeh is the out of focus stuff, and the more out of focus it is, the better the bokeh.

If being out of focus is the real issue, then the factors that will give you the most out of focus backgrounds are:
1. size of relative aperture (the f-stop) (smaller numbers are larger apertures--thinner depth of field)
2. focal length of lens (the longer the lens, the thiner the depth of field at any given aperture) [Note--you said the longer lens gets out of focus background only zoomed in--which is to say, longest focal length]
3. distance of camera to subject (the closer the subject, the more out of focus the background)
4. distance of subject to background (the farther, the less focused)
5. size of film or sensor (camera format--the bigger the sensor, the less depth of field at given settings)
6. degree of enlargement of the photo and the distance for viewing it (billboards may look sharp in the background from a distance)

For softest background, use longer lens, close to subject, with distant background, using the largest aperture. (But there are other things to consider for artistic purposes.)

But note--the shape of the aperture neither increases nor decreases the severity of the out-of-focus background; rather (some say) it somehow enhances the quality of such backgrounds in a way that only the word "bokeh" is meant to capture. If someone says a certain lens or lens series had good bokeh, it is not clear what they mean, but they probably just mean it had a round aperture with many blades, and they (somehow) see this in the pictures. To me, it is significant that nobody could see this until the word "bokeh" was picked up from the Japanese, not even experts. Some people still can't see it. I don't think Ansel Adams mentioned it in his 5-volume textbook series, maybe because he did not speak Japanese.

Apaflo Loc: Anchorage, Alaska

None of that, not one word, is correct.

Bokeh is the character or quality of out of focus areas.

It is unrelated to perspective compression.

Certainly both focal length and aperture may have some specific effect with any given lens, but another lens might exhibit exactly the opposite effect! A given change to one lens may cause harsher bokeh and the same change on a different lens may cause smoother bokeh.

Any given lens does not, indeed cannot, produce more bokeh or less bokeh than another lens, because there simply is no such thing as quantity of bokeh.

All of the stated characteristics are applicable to out focus blur, which many people very mistakenly confuse with bokeh. Blur has a quantity. It also has a quality... which is called bokeh!

RWR Loc: La Mesa, CA

What would you call the quality of out of focus foregrounds?

RichardTaylor Loc: Sydney, Australia

Highlights are smoth and rounded and are not hexagons.

SharpShooter Loc: NorCal

Mike, welcome to the Hog!
I'll assume you are talking about DoF and not bokeh.
This wil probably not answer your question but if you can understand it, it might help.
DoF is purely optical physics and not lens specific but lens focal length does come into play.
Here goes:
Lenses produce their minimum DoF at their minimum focus distance.
All lenses will produce the same DoF if they are at the same relative focus distance, and at the same f-stop.
The relative minimum focus distance is 4x as long for a 200mm lens as a 50mm lens(the 200 is 4 times longer).
So if you have a 17mm prime and a 17-55 zoom, both at f4, they will both have the same DoF at 17mm at the same distance.
If you have a 50mm and a 200mm, both at f4, and at their relative minimum focus distance, is say 2 feet vs 8 feet both will have the same DoF at those minimum focus distances.
But, after that they will start to diverge.
Probably doesn't make any sense, does it??
SS

RichardTaylor Loc: Sydney, Australia

See this post - it's mine here on UHH

http://www.uglyhedgehog.com/t-504341-1.html#8514762

Apaflo Loc: Anchorage, Alaska

Or foregrounds!

A lot of different lens characteristics contribute to bokeh, but one of the most interesting is spherical aberration. If it is perfectly balanced the effect on the foreground and background will be the same. If spherical aberration is under corrected an out of focus point of light in the foreground will be a solid globe of light but the outer part will be a brighter circle than the center. The background will have a dimmer outer edge and brighter center. If spherical aberration is over corrected the front and back effects are the opposite.

One oddity of the above is that over correction may appear to be sharper, while under correction will generate better boken in the background.

bmike101 Loc: Gainesville, Florida

is this round or hexagonal? I can't really tell. when I zoom in on it I seem to see hexagons but that might be an illusion.

(Download)

RichardTaylor Loc: Sydney, Australia

IMHO that's just shallow depth of field (zone of sharpness)

blackest Loc: Ireland

hmm being out of focus is one thing which is related to focus distance, aperture, sensor size , and probably focal length (maybe not but its easier to blur backgrounds with longer focal lengths )

Maybe bokeh is best translated as beauty. Some background blur is more beautiful than others ... kind of explains why it is hard to measure and quantify.