Bokeh

[boyyocool]

I've read this word many times and I seem to not fully understand the term...according to me all lenses cannot produce bokeh...Am I right? If wrong please correct me and also I would like to know what is the perfect focal length to produce bokeh Finally what does bokeh depend upon?

[Andrew1]

All lenses have bokeh. It's a generic term for the out of focus areas in the background of a photo. Shape and details of the blurring are primarily caused by the number of blades in the diaphragm but can also be contributed to by the light at the time or even a pattern placed over the lens. There's a number of things. Some people who pay attention to such matters like that imply there are bokeh's that are better than others. Some of use just don't care either. For a more in-depth explanation check around on a search engine and you'll find many explanations. For a start...

http://en.wikipedia.org/wiki/Bokeh

Have fun.

[Glenn NK]

Although the following article is called Bokeh Test, and it comes as close as any to defining bokeh (sometimes spelled boke), or at least it shows what it can be. There are no measurements for bokeh so it is somewhat subjective, however it is real, and bad cases of bokeh are really bad.

The article uses testing to demonstrate what bokeh is (I've referenced this article several times, and I suspect that many people don't follow it right through - it took me a few tries).

http://www.rickdenney.com/bokeh_test.htm

The article linked to by Andrew is also very worthwhile.

Glenn

[Black Pearl]

A definitive guide:

http://www.zeiss.com/c12567a8003b8b6f/embedtitelintern/cln_35_bokeh_en/$file/cln35_bokeh_en.pdf

[Dave Humphries]

Although the following article is called Bokeh Test, and it comes as close as any to defining bokeh (sometimes spelled boke), or at least it shows what it can be. There are no measurements for bokeh so it is somewhat subjective, however it is real, and bad cases of bokeh are really bad.

The article uses testing to demonstrate what bokeh is (I've referenced this article several times, and I suspect that many people don't follow it right through - it took me a few tries).

http://www.rickdenney.com/bokeh_test.htm

Hi Glenn,

Not seen that before, apart from being a little dated in terms of lenses tested, it is, as you say, very good with practical demonstration images.

It is the first I have seen that mentions the double edge on linear highlight picture elements and shows it - this is an area I find a problem on the Nikon 70-300mm, although I obviously need to test at various apertures and focal lengths. With a bird shot against the sky, it is fine, but put some sunlit light-straw coloured grasses behind it and it can get nasty, definitely requiring the application of sharpening selectively on the subject only, if I don't want to make it 5x worse.

EDIT: Whoa Robin, I'm gonna need a coffee and a clear head to read your link , but that looks very educational from the quick skim I have had so far.

Thanks all,

[Dave Humphries]

Another thing that has me wondering - since some of the 'tech speak' discusses the effect Chromatic Abberation (CA) correction of lens' design has on bokeh - what effect does the software correction of CA (and other lens defects) have on bokeh? e.g. the corrections in LR/CS5 (ACR) or one of the plugins like PTLens.

[Glenn NK]

A definitive guide:

http://www.zeiss.com/c12567a8003b8b6f/embedtitelintern/cln_35_bokeh_en/$file/cln35_bokeh_en.pdf

Robin:

We would really appreciate a summary of this article is you would do that.

Glenn

[arith]

I've been looking at this question for about a day now; it is true the better the lens the better the bokeh, and rounded aperture leaves are better than straight ones.

But I think it has something to do with reflected light, not 100% but mostly. Reflections or diffraction in water can be attractive, and I sometimes try to exploit that.

[boyyocool]

So much info! Lot to digest! thnks guys!

[Black Pearl]

Robin:

We would really appreciate a summary of this article is you would do that.

Glenn

Hahaha!
How many pages did read before a headache made it blur......all be it a beautiful Zeiss bokeh blur?

[Glenn NK]

Hahaha!
How many pages did read before a headache made it blur......all be it a beautiful Zeiss bokeh blur?

The blur set in rather quickly.

What I found interesting in the article I linked to was at the very bottom under the heading, "What have we learned"?

Point number 10 is interesting: "Aperture shapes are not really an issue with bokeh, especially near wide open. In none of these tests, was aperture shape the main determinant in apparent bokeh quality. So, we should stop counting aperture blades. The lens with the most aperture blades was the B&L Tessar, but it had uniformly the worst bokeh."

Glenn

[tclune]

Point number 10 is interesting: "Aperture shapes are not really an issue with bokeh, especially near wide open. In none of these tests, was aperture shape the main determinant in apparent bokeh quality. So, we should stop counting aperture blades. The lens with the most aperture blades was the B&L Tessar, but it had uniformly the worst bokeh."

It's interesting, but wrong. True, in the images that he used as examples, the aperture shape was not an issue. However, it is VERY common in, e.g., out of focus points of light for the aperture blades to be the dominant source of ugly bokeh. We have all seen stop sign shaped OOF light points, which are directly due to using too few and too straight aperture blades. The other ugly point source bokeh -- where the light blob looks like a donut -- is not a matter of aperture blades, but astigmatism of the lens AIUI.

[Glenn NK]

Question about aperture shape:

Is it the shape of the aperture blades that creates the bad bokeh, or is it the lens design that causes bad bokeh, and because of this, the shape of the aperture is then noticeable?

Glenn

[Black Pearl]

Its a Hell of a complicated article but read the Zeiss one I posted - it will explain EXACTLY what attribute to good/bad bokeh.

[Glenn NK]

Its a Hell of a complicated article but read the Zeiss one I posted - it will explain EXACTLY what attribute to good/bad bokeh.

Robin:

I agree. And have you a quick summary for those of us less inclined to delve into Zeiss's reader friendly treatise?

Glenn

[Dave Humphries]

First I'll answer Krishna's questions (which I have 'lettered' for reference);

I've read this word many times and I seem to not fully understand the term...according to me all lenses cannot produce bokeh...Am I right? If wrong please correct me

That's a tricky one to answer because of the common mis-use of the word "Bokeh". Strictly speaking, it refers to the quality of the out of focus areas of an image. A few might argue that if the quality is bad, it 'doesn't have bokeh' like saying a Rolls Royce is a 'quality car', but that a cheaper brand isn't. However, I would say all lenses have bokeh, some have 'good bokeh' and some 'bad bokeh'. I suppose, being pedantic, if you were to shoot an image where absolutely everything is in focus, you could say an image has no bokeh, because you cannot have a quality for something that doesn't exist in the shot.

I would like to know what is the perfect focal length to produce bokeh

bokeh doesn't occur at one focal length any more than another, not unless you get into the detail of how a specific zoom lens performs for bokeh at different focal lengths. It could be argued that telephoto lenses with their narrower Depth of Field (DoF), so with a typical subject, you'll get more out of focus areas with one to display the good or bad bokeh in. The aperture used has a more direct effect on the amount of bokeh (there you go, I just mis-used the word), since use of a wider aperture produces more blurriness.

Finally; what does bokeh depend upon?

the design of the lens (more complex than just the number and shape of aperture blades), but the subject and background being shot will greatly affect what you see in the image.

~ have you a quick summary for those of us less inclined to delve into Zeiss's reader friendly treatise?

OK, I'll bite as Robin seems unwilling

I have extracted the pertinent sentences, usually the ones the author (H. H. Nasse) put in bold himself.

Depth of field is based on the acceptable blurriness and is therefore essentially based on arbitrary specifications. (p.3)

Reducing the size of the film format therefore reduces the depth of field by the crop factor. (p.9) - this answers/confirms the FF DoF thread question

In fact there is a table of equivalent f/numbers for different sensor sizes (p.10)

All formats have the same depth of field at the diffraction limit. (p.17) I hadn't thought of it this way, but I guess that makes sense, although it is a bit like saying 'when all things are equal, everything is the same'

The root of the Japanese word "boke" or "bokeh" actual means nothing good; its meaning is similar to "confused" or "dizzy" and is used to name mental states in exactly the same way. In photography the term ”confused“ relates naturally to light beams which no longer come together at a single point in an orderly manner. (p.25)

All the parameters listed here influence the phenomena outside the focal plane: (List p.25)
• Picture format
• Focal length
• f-number
• The camera-to-subject distance
• Distance to the background or the foreground
• Shapes and patterns of the subject
• Aperture iris shape
• Aberrations of the lens
• Speed of the lens
• Foreground/background brightness
• Colour

That's about it without delving into the example images, graphs, diagrams and formulae
(and that's above my pay scale)

How much of a problem bad bokeh is, is open to interpretation, not least because it is subjective, so different people will have different views on what is acceptable.

If you shoot birds against the sky, it's not much of a problem is it?

Cheers,

[arith]

[Glenn NK]

My hat's off to Dave Humphries for his post.

Very well done.


Glenn

[ap.photo]

oh and one more little tidbit for thought....

Bokeh is determined by your aperture aka f-stop. well. i could take that 35mm and shoot at f/2. then take the 135mm and shoot at f/2. i could shoot a subject, and frame them the same way in both shots (the body fills the frame from head-to-toe), BUT the pictures would look very different. the bokek/background blur would be very different. why? i'm shooting at the same aperture, right? why the difference in the appearance of the image? why isn't all bokeh created equal?

Anyone?

[rpcrowe]

A smooth "creamy" bokeh is usually considered the nicest by many photographers, primarily because it doesn't have any significant details to conflict for attention with the main subject.

There are some lenses which produce very smooth bokeh. My 70-200mm f/4L IS lens has rounded aperture blades that produce exceptionally smooth bokeh...





The 70-200mm f/2.8L IS ii lens also incorporates rounded aperture blades which, supposedly, also produce very smooth bokeh...