Don’t Mistake Depth of Field With Bokeh

Don’t Mistake Depth of Field With Bokeh

Often, I see the term "bokeh" being used when "depth of field" is meant. That’s wrong, simply because it is not the same. Although many will understand the distinction between the two, I will explain the difference for those who do mistake depth of field with bokeh.

Before I dive into the difference between depth of field and bokeh, I would like to explain the two definitions first. As you will notice, it will automatically make clear how the two are related but not the same. Let me first start with depth of field.

Depth of Field

Most of us understand the concept of depth of field. It’s the area in front of and behind the focal plane that has acceptable sharpness. In other words, the area that falls inside the depth of field boundaries will appear sharp to our eye, depending on the print size and viewing distance.

A tree frog, shot with a 100mm macro lens at f/5.6. The print size and viewing distance will also influence the depth of field in this image.

Depth of field can be manipulated by changing the aperture, but the distance to our subject and its relative distance to the background also has an influence on the way depth of field is rendered. 

A small depth of field is achieved by using a 35mm lens and f/1.4. The appearance of the out-of-focus area is called bokeh.

To keep it as simple as possible, let’s just focus on the effect of the aperture and ignore the other important variables that define depth of field. The smaller the aperture becomes, the larger the depth of field will be. A large aperture will make the area that has an acceptable focus narrow. Everything in front of that narrow focus area will be blurred, just like everything beyond the focus area.

By using a small depth of field, the image can get a nice 3D effect. I used a Canon EF 85mm lens and f/1.2 for this image. The out-of-focus area has a nice and smooth appearance with this lens.

Bokeh

The way these blurred areas in front of and beyond the in-focus areas appear is determined by the build and quality of the lens you are using. Every lens has its own characteristics, rendering a unique out-of-focus area. The appearance of this out-of-focus area is called bokeh.

The appearance of the out-of-focus area in an image is called bokeh. Points of light can be transformed into large rings.

Bokeh derives from the Japanese word "broke," which means blur or haze. The addition of the letter H was first introduced by Photo Techniques magazine editor Mike Johnston, to force a correct pronunciation for non-Japanese speakers. Today, the term is defined as the way a lens renders out-of-focus points of light.

Bokeh can be important when shooting macro, like in this example, where the out-of-focus area takes part in the composition. I used a small depth of field to get a nice bokeh.

There is no quantification for bokeh. The way a lens renders out-of-focus areas is subjective to personal preferences. Still, some lens designs will produce a less pleasing out-of-focus area, which becomes more apparent when a shallow depth of field is used.

As mentioned, the lens design will determine the bokeh. The amount of aperture blades has a big influence. Fewer aperture blades will produce a polygonal shape of the out-of-focus light points, and the curvature of the aperture blades will determine the edge hardness.

The appearance of the out-of-focus area depends on the quality of the lens and the lens design itself. This example shows how the bokeh is different for each lens.

The appearance of the out-of-focus light points is also influenced by spherical aberrations, lens distortion, and lens design in general. But remember, what one considers nice-looking bokeh is personal. Some will like the bokeh of a certain lens, while others may not.

The difference in bokeh between two Sony lenses at the same focal length and aperture. Although the depth of field is similar, the appearance of the out-of-focus areas is different.

The Relation Between Depth of Field and Bokeh

Although bokeh is the term for the way a lens renders out-of-focus points of light, it doesn’t matter how much out of focus these points of light are. In other words, bokeh is also present with a larger depth of field. But the bokeh will have a completely different appearance.

The small depth of field makes the wild orchid stand out of its surroundings. The appearance is determined by the lens design. This Canon EF 70-200mm lens shows attractive bokeh at f/2.8.

In general, the bokeh becomes much more pleasing to the eye when the depth of field becomes narrower. In this way, we can see a sort of relation between the depth of field and bokeh. I think that's the reason why some mistake depth of field with bokeh. They assume it's only present when the smallest depth of field is achieved. 

Just remember: depth of field determines the plane of focus. Bokeh is the aesthetic appearance of the out-of-focus area.

Although bokeh is just a aesthetic term for the appearance of the out-of-focus area, a narrow depth of field can produce nicer-looking bokeh.

Manipulating the Bokeh

There are ways of manipulating the bokeh of a lens. One recent example is the Canon RF 100mm f/2.8L macro lens, which incorporates a SA control ring. It will change the way out-of-focus points appear in the image. You can read more about this lens in my review here on Fstoppers.

The SA control ring on the Canon RF 100mm f/2.8 macro allows you to control the appearance of the out-of-focus areas, as shown in this example.

This is not the only example of a lens that enables you to change the bokeh. Other examples are the Minolta/Sony STF 135mm f/2.8 and the Nikon 105mm DC-Nikkor. Some lenses have truly unique bokeh, like some Meyer Optik Görlitz lenses, which show soap bubbles for out-of-focus light points. Another strange bokeh type is produced by mirror lenses.

A mirror lens has a small mirror in the center of the lens, producing the characteristic donut shape of the out-of-focus light points. This image was taken with an old Russian MTO 1000A mirror lens.

There are also ways of changing the appearance of the bokeh by introducing creative cut-out forms that can be held in front of a lens. These forms can be bought in shops, or you can make these yourself by cutting out your shapes from a piece of paper. This way, it is possible to change the shape of the out-of-focus light point in an extreme way. It’s also something you could play with during the long winter nights, in addition to the things I mentioned in my previous article.

If you're feeling creative, you can shape the bokeh of your lens by placing all sorts of cut-out shapes in front of your lens.

The effect with the cut-out forms will be more pleasing if the lens you are using already has attractive bokeh. By changing the depth of field, you can change the size of the out-of-focus forms until the effect you’re pleased with emerges.

Don’t Mistake Depth of Field With Bokeh Ever Again

To sum things up, depth of field and bokeh are two different things altogether. The former is about the area that has acceptable focus. The latter is the aesthetic quality of the out-of-focus area.

A portrait with a small depth of field (85mm and f/1.4). The lens shows a nice and smooth background. In other words, this lens has great bokeh.

Bokeh is also present with large depth of field, but it will generally become more pleasing to the eye when a small depth of field is used. This can be considered a sort of relation between the two. Unlike depth of field, bokeh can’t be quantified but is subject to personal preferences.

What lens do you think has the most beautiful bokeh? If you have an example image made with that lens, please post it in the comment below. I’m looking forward to your replies.

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12 Comments
Bruce Spear's picture

Bokeh comes from the Japanese word boke (ボケ) not "broke."

Tom Reichner's picture

Yeah, I was really surprised to see the most key word in the entire article misspelled. If careful proofreading isn't going to catch that, then what is it going to catch?!

Nando Harmsen's picture

Automatic spelling control is responsible

MC G's picture

Splitting hairs.

winzehnt gates's picture

Try a Tokina 400mmF8 mirror lens with its onion ring bokeh. Then come back and tell us again that differentiating between DOF and bokeh were "splitting hairs".

Indy Thomas's picture

The people obsessed by bokeh are scarcely going to concern themselves with the details.

The problem is a world where people spend twenty minutes on YT and then start advertising for work.
No real interest in the craft but rather they delight in "learning the tricks" that they think will translate into a career of riches and glamour.

Rhonald Rose's picture

Nice, although I knew it, I never thought about it. Useful write-up.

Tom Reichner's picture

Bokeh and depth of field are not two separate things. They are two different things, but they are not at all separate. They are closely tied to one another. If you change the depth of field of an image, then you are changing the bokeh. I mean, the quality and visual characteristics of the out-of-focus areas will change if you change the depth of field.

Hence, it makes sense to think of these two things as being inextricably linked, rather than as two independent entities within an image.

In practice, this means that we should be aware that changing the depth of field will have an effect on the bokeh. For instance, if I want to increase the depth of field so that I get the entire Deer in focus, instead of just the front half of the Deer being in focus, then I need to understand what effects that is going to have on the way that the blurred-out vegetation behind the Deer is rendered. I cannot change one without changing the other.

Matt Rennells's picture

The Nikkor 105 DC (and the 135 DC) do not have a ring to control bokeh but actually the depth of field. Most lenses have part of their depth of field in front of and behind the area that is focused on (something like 30% in front and 70% behind). The controls on the DC lenses let you move that depth of field forward or backwards without changing the location of the focused point. This is very helpful shooting in bright sun as you can shoot at f/5.6 and shift the focus so that the background blurs more and it looks more like you're shooting at f/2.8 (while still having a sharp subject). This only really works with a DSLR using a mirror and separate focusing system (not focus on a chip like mirrorless). So as the article title suggests you are confusing bokeh and depth of field with those lenses in particular.

David Guijarro's picture

Recommendations for a nice bokeh according to my criteria for Apsc from Fuji X: Meyer Optic Gorlitz Oreston 50f1.8 (fantasy), Kamlan 50f1.1 mkII (pure watercolor) and 7artisans 35f0.95 (bubbles).

Przemek Lodej's picture

As I'm reading this I'm wondering why there is no mention of the old Russian Helios-40-2 85mm f1.5 or Helios 77M-4 50mm F1.8 lenses. For all the bokeh freaks these lenses are legendary.

Black Z Eddie .'s picture

They're too busy, distracting, and dizzying.

https://www.youtube.com/watch?v=dDe1_-XS3gc