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Bokeh, Background Blur and Focal Length
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PostPosted: Sun Sep 01, 2019 5:50 pm    Post subject: Bokeh, Background Blur and Focal Length Reply with quote

Many decades ago, the term "bokeh" was established by Japanese lens connaisseurs to distinguish between different shapes of the background (and to a lesser extent the foreground) blur.

The following example - coloured glass windows in a Swiss church - shows "bad bokeh" (often also called "noisy") on the left side, whereas the image on right side is considered as a "good" or "smooth" bokeh.



Quite often the term "bokeh" these days is used in a less precise way, simply referring to the amount of backgrund blur (and not to its quality, as stated above):



Apart from a few old lenses with a really noisy bokeh (Meyer Trioplan, Leitz Thambar) and a few speciality lenses with a distinctively smooth bokeh (mainly the Minolta STF 2.8/135mm STF and its derivatives), the differences between lenses of the same focal length usually are rather subtle.
The following image shows the bokeh of twelve different normal lenses (made by nine manufacturers) with speeds of f1.2, f1.4 and f1.7:






Much more important for the general impression of an image is the focal length used:



I hope these images can help to clarify some ambiguities about the use of term "bokeh".

Stephan


PostPosted: Sun Sep 01, 2019 7:31 pm    Post subject: Reply with quote

To me, there are no ambiguities. "Bokeh" is a term that refers to OOF highlights. It is non-judgemental. People will assign qualities to types of bokeh, as per your reference to "noisy" and "good" or "smooth," some might even say "pleasing" bokeh. But the term "bokeh" by itself holds no such connotations.

The ambiguities appear when folks begin to discuss bokeh quality. As the old saying goes, "There's no accounting for taste." So I would argue that "good" bokeh is whatever a person considers is good bokeh. Another may disagree, but then it becomes a matter of taste, which involves individual preference.


PostPosted: Sun Sep 01, 2019 9:07 pm    Post subject: Reply with quote

Maybe so, but clearly the focal length does indeed change dramatically the OOF picture as illustrated above...

I came across this observation with the Minolta 100-500 f8 I recently received.
This works wonders for background as it reduces the captured area in the background (smaller angle).
Steve demonstrates it quite clearly with his shots.

Of course, mirror lenses do add complexity in the background with donut shapes


PostPosted: Sun Sep 01, 2019 10:10 pm    Post subject: Reply with quote

Antoine wrote:
Maybe so, but clearly the focal length does indeed change dramatically the OOF picture as illustrated above...


Yes, but that isn't the only factor involved in producing dramatic bokeh. An equally important dynamic, I would argue, is maximum aperture. I have a few f/1.2 lenses that have such razor thin depths of field when wide open that I have to pay extra careful attention to my back and forth movement as I'm taking pics. The slightest forward or rearward movement can render an out of focus subject. So obviously, it is possible to entirely blow out the background if positioning the subject correctly against the background with these lenses.

Case in point:

Canon 85mm f/1.2 SSC Aspherical wide open. Subject at MFD, background leaves maybe two feet distant?


Canon 55mm f/1.2 SSC. Subject at MFD, background leaves same distance as above. Note the similarities in level of background blur, despite the substantial difference in focal lengths.


Last edited by cooltouch on Sun Sep 01, 2019 10:16 pm; edited 2 times in total


PostPosted: Sun Sep 01, 2019 10:13 pm    Post subject: Re: Bokeh, Background Blur and Focal Length Reply with quote

I guess by default bokeh should mean "back (as in behind the subject) bokeh"
Otherwise some lenses are pretty weird, like the the overcorrected
stevemark wrote:
Apart from a few old lenses with a really noisy bokeh (Meyer Trioplan)

Trioplan has very smooth front bokeh.


For reasons I'm not entirely prepared to explain, some lenses have distinctly different qualities in rendering "plain" (as in: brick wall) and rich OOFH (out-of-focus highlights) (as in: tree leaves canopy) backgrounds.
To my eye Hexanon 58/1.4 is very good with plain backgrounds, but quite weird with OOFH.
Another such example is Zuiko 50/1.4. While being famous for unique "bad" OOFH, it's actually tiny bit smoother than Minolta MD-III 50/1.4 with brick walls.


The more WOW factor (focal length divided by the F-stop) lens have, the more blur you can expect.
It's actually a lot cheaper to increase focal length than F-stop where possible.
50/1.2 lens has WOW 41.6 which sounds mighty impressive, until you realise 58/1.4 has a WOW 41.4 for the fraction of the price.
What I've noticed is: not all lenses are created equal and more bokeh quantity does not equate to smoother background.
Which brings to the table another lens characteristic I call bokeh quality.
Lens with significantly better bokeh quality is able to deliver smoother background even if it lags significantly in WOW/quantity.



It gets weirder. You may not even need a different lens to compare.
In some lenses bokeh quality is very sensitive to aperture and improves with stopping down.
For some only the first stop yields noticeable results: like the ill-famed (in terms of bokeh) Canon FDn 50/1.4.
Others show significant improvement with a second aperture stop too: this would be a Minolta Rokkor 58/1.4.



It gets even more weirder. The bokeh quality is not uniform across the frame.
This isn't just about the mechanical vignetting of OOFH (i actually happen to like that), but overall bokeh quality deteriorates towards the corners due to astigmatism and coma (but it seems like not all undercorrected coma is bad)


(Corner bokeh deterioration with Minolta MC Rokkor-PG 50mm F1.4)




And we are still not deep enough the rabbit hole.
Some lenses show distinctly different bokeh quality depending on focus distance.


(Olympus Zuiko 50mm F1.8, feeling pretty smooth)


(Olympus Zuiko 50mm F1.8, looks very different now)

Woah, what did just happened here? Was it truly the same lens at the same aperture? Yes.
Was it caused by less bokeh quantity due to longer focus distance? No. Sort of yes, but no.

My explanation is: Zuiko 50/1.8 is fairly neutrally corrected for spherical aberrations close to the MFD and quickly becomes overcorrected at longer focus distances.
If you are a fan of "3D-pop", you might want to seek exactly this behaviour. Sadly, doesn't help with bokeh quality.



Overall, this is a big topic. If your mind isn't blown yet, let me fetch my focal reducer real quick:


(Olympus Zuiko 50mm F1.4)

(Olympus Zuiko 50mm F1.4 on Lens Turbo II focal reducer)

Shocked


And we haven't touched front bokeh, front-to-back bokeh transitions, coma rendering and probably a whole host of things I don't even know about yet.




"Nervous bokeh" is not necessarily "bad", but one has to have a taste for it.
I'm personally guilty of liking some pretty weird lenses which just can't be proclaimed "good".


(Minolta MD-III 50mm F2 selective frequency filtering in bokeh)




(Widely popularised weirdness of Helios 44-2/44M-X 55mm F2. It's actually can be pretty smooth if you look past the swirly bokeh)




(Jupiter-8 50mm F2 asked to check in. It's bad technically, but I can't stop looking)


PostPosted: Mon Sep 02, 2019 1:37 am    Post subject: Reply with quote

"Many decades ago, the term "bokeh" was established by Japanese lens connaisseurs..."

Let's see the example images they used then to describe bokeh. Your examples are merely your guesses. Smile

Bokeh was defined as blur in that decades-old magazine. Highlights are not blur. Out of focus is not blur, yet blur is out of focus. The blur has a pattern yet nothing can be distinguished. An out of focus tree in the background is not bokeh because the tree can be distinguished. Using the definition, only a very few of your examples show bokeh, such as the right image in the second pair. Objects can be distinguished in the background of nearly every image, thus they do not exemplify bokeh.

Michael's bud images are examples with bokeh.


PostPosted: Mon Sep 02, 2019 5:03 am    Post subject: Reply with quote

I dunno. I think maybe you're being too restrictive. Would you say that the background "blur" in the following image is not bokeh? The parallel lines are a metal park bench.

Canon F-1, Canon FD 85mm f/1.2 Aspherical @ f/1.2, Kodak Elite Chrome 100


PostPosted: Mon Sep 02, 2019 8:50 am    Post subject: Reply with quote

That's bokeh. Before you told me I couldn't distinguish a bench. You could be lying I wouldn't know.

I think rather than being restrictive, the term is used too loosely and incorrectly to describe other effects such as oof highlights, flare, bloom, or simple oof where contents are discernable.


PostPosted: Mon Sep 02, 2019 11:56 am    Post subject: Re: Bokeh, Background Blur and Focal Length Reply with quote

aidaho wrote:

The more WOW factor (focal length divided by the F-stop) lens have, the more blur you can expect.
It's actually a lot cheaper to increase focal length than F-stop where possible.
50/1.2 lens has WOW 41.6 which sounds mighty impressive, until you realise 58/1.4 has a WOW 41.4 for the fraction of the price.


What you call "WOW fator" is just the size of the entrance pupil. For most lenses (the exceptions are the wideangle lenses), when the lens is wide open, the entrance pupil is generally given by the diameter of the front optical element.


PostPosted: Mon Sep 02, 2019 1:41 pm    Post subject: Reply with quote

visualopsins wrote:
I think rather than being restrictive, the term is used too loosely and incorrectly to describe other effects such as oof highlights, flare, bloom, or simple oof where contents are discernable.


But you see, that's been my point. It is inherently a loose definition. Bokeh has been defined as "the way the lens renders out-of-focus points of light". That's a very general description, you ask me. I would further argue that it not be limited to OOF points of light, but anything that is OOF in an image. Those blurred leaves in my above photos are not points of light, but I suspect few people would claim that they are not part of the bokeh of the images.

Are the blurred leaves in the following image points of light? Maybe some folks would say yes, but to me they're just OOF leaves.

Canon XS @ ISO 100, Canon FD 85mm f/1.2 @ f1/2. glassless FD to EOS adapter.


PostPosted: Mon Sep 02, 2019 3:56 pm    Post subject: Reply with quote

cooltouch wrote:
visualopsins wrote:
I think rather than being restrictive, the term is used too loosely and incorrectly to describe other effects such as oof highlights, flare, bloom, or simple oof where contents are discernable.


But you see, that's been my point. It is inherently a loose definition. Bokeh has been defined as "the way the lens renders out-of-focus points of light". That's a very general description, you ask me. I would further argue that it not be limited to OOF points of light, but anything that is OOF in an image. Those blurred leaves in my above photos are not points of light, but I suspect few people would claim that they are not part of the bokeh of the images.

Are the blurred leaves in the following image points of light? Maybe some folks would say yes, but to me they're just OOF leaves.


Well, no, bokeh was defined as blur according to the old magazine article. Out of focus points of light are called highlights. Oof areas are oof areas. Bokeh blur is oof, but oof is not necessarily bokeh. In the image the points of light, highlights, are in between the green blur of the leaves. The leaves are indistinguishable therefore here we have bokeh with highlights.


PostPosted: Mon Sep 02, 2019 7:55 pm    Post subject: Reply with quote

visualopsins wrote:

Well, no, bokeh was defined as blur according to the old magazine article. Out of focus points of light are called highlights. Oof areas are oof areas. Bokeh blur is oof, but oof is not necessarily bokeh. In the image the points of light, highlights, are in between the green blur of the leaves. The leaves are indistinguishable therefore here we have bokeh with highlights.


If we get back to original definitions, then we must get back to the Japanese word [boke], which means 'blur' or 'haze.' It has only been once photographers got a hold of the term that the definition shifted. The definition that I've always used is "out of focus highlights," but upon further examination of some of my own photographs, I'm not even so sure of my own definition anymore.

In the above image of a rose, I think you are misinterpreting it. Those bright patches were leaves. The darker areas were areas between the leaves. The photo was taken on a sunny day and the leaves were doing a pretty good job of reflecting the sunlight. But still, I find myself hesitating over referring to those leaves as highlights -- especially when you're stating that highlights are points of light because these leaves are not points. But I guess if I wanted to get picky about it, the leaves are highlights -- just not points of light types of highlights.


PostPosted: Mon Sep 02, 2019 8:58 pm    Post subject: Reply with quote

Personally, I don't dive into nuances.

In focus = not bokeh.
Out of focus = bokeh.

In focus, going out of focus = transitional area.


PostPosted: Tue Sep 03, 2019 12:59 pm    Post subject: Reply with quote

Bokey Hokey! I'm fed up of seeing horrible pictures with messy, swirly backgrounds. Without the word, you wouldn't have the phenomenon.


PostPosted: Tue Sep 03, 2019 6:19 pm    Post subject: Reply with quote

??? That's saying essentially that a physical property doesn't exist because there's no name for it. If bokeh wouldn't have been coined, some other word or noun phrase would have.


PostPosted: Tue Sep 03, 2019 7:10 pm    Post subject: Reply with quote

cooltouch wrote:
??? That's saying essentially that a physical property doesn't exist because there's no name for it. If bokeh wouldn't have been coined, some other word or noun phrase would have.


Perzactly! lol

All those terms such as highlights, flare, coma, bloom, oof, & etc., didn't make coining bokeh necessary. The definition of bokeh is quite limited. The term is general however, describing many sometimes wildly different examples, hence the confusions. Bokeh describes something not described by or including what those other terms describe. For example we say "bokeh with highlights", not simply "bokeh" to describe that. When the shape of the aperture is seen, that's a highlight, not bokeh.


PostPosted: Tue Sep 03, 2019 10:03 pm    Post subject: Reply with quote

You know what? I'm done disagreeing with you people. Y'all call it whatever you want and so will I -- and let confusion reign.


PostPosted: Wed Sep 04, 2019 9:01 am    Post subject: Reply with quote

cooltouch wrote:
You know what? I'm done disagreeing with you people. Y'all call it whatever you want and so will I -- and let confusion reign.


I'm with you on that Michael, sometimes it is best to just let go Wink


PostPosted: Wed Sep 04, 2019 2:49 pm    Post subject: Reply with quote

kds315* wrote:
cooltouch wrote:
You know what? I'm done disagreeing with you people. Y'all call it whatever you want and so will I -- and let confusion reign.


I'm with you on that Michael, sometimes it is best to just let go Wink


Has been said here before "mother of idiots is always pregnant" whatever that means.


PostPosted: Wed Sep 04, 2019 3:05 pm    Post subject: Reply with quote

From local photographer William Pierson http://www.williampierson.com/image_gallery_Visions.html


Wave Moment by William Pierson

(edit: flare, clouds in background, not bokeh.)


Last edited by visualopsins on Wed Sep 04, 2019 9:37 pm; edited 1 time in total


PostPosted: Wed Sep 04, 2019 8:42 pm    Post subject: Reply with quote

Seems yet another thread that needs a link to the original articles that describe bokeh and what it really is and introduced it to the Western world.

https://drive.google.com/open?id=1AD8kuNpvUogMopyb_lAv2ZCG_HFWb8qp


PostPosted: Mon Sep 09, 2019 6:23 pm    Post subject: Reply with quote

We are agreed: many do not understand the word bokeh. Bokeh & Depth of field are often conflated in observers' commentaries. The difference between the 2 is straightforward.

DOF is determined by 3 factors:

1) proximity to subject --(the closer to the subject, the shallower the DOF
2) aperture -- (larger the aperture, the shallower the DOF)
3) focal length --(longer the focal length, the shallower the DOF)

Bokeh (as Michael said in the 1st response here) is determined by how a lens transitions in-focus to out-of-focus areas. Since subject isolation is important to photographers, the less obtrusive the (transitions), the better the bokeh.
jt