Bokeh explained by Steve Cushing Photography

BOKEH

In photography, bokeh (/ˈboʊkə/ BOH-kə or /ˈboʊkeɪ/ BOH-kay;[1] Japanese: [boke]) is the creative aesthetic quality of the blur produced by making use of the DEPTH OF FIELD (Click for more information) to alter out-of-focus parts of an image. Bokeh has also been defined as "the way the lens renders out-of-focus points of light". Differences in lens glass aberrations and aperture shape cause very different bokeh effects. Some lens designs blur the image in a way that is pleasing to the eye, while others produce distracting or unpleasant blurring ("good" and "bad" bokeh, respectively).

The funny thing is the Japanese term "bokeh" has become almost universally known in the English speaking photography community as a term for “out of focus blur”. But in recent years Japanese photo writers have evidently decided they need a cool new loanword instead of bokeh, so one now often sees the fractured English expression "outo fokasu” a distortion of the English term "out of focus".

Video that explains Bokeh

WHAT EFFECTS BOKEH

First the Focal Length of the Lens

The longer the focal length of the lens, the easier it is to blur the background and increase the degree of blur.

Crop Factor

The images on this site have been taken with a full frame sensor. If you use a camera with a crop factor this will increase the depth of field and change the focal length of the lens. The bokeh will therefore change.

Aperture Range.

The larger the relative aperture (the smaller the F number), the easier it is to achieve strong blurring of the image in the non-sharpen area and increase the blur outside the depth of field.

Because increasing or decreasing aperture changes the size of the hole that the light passes through in your lens, it also changes the size of the bokeh. An aperture of f22 is small, so the bokeh shapes will be small. F1.2 will create large bokeh shapes by comparison. Most photographers go for a wide aperture when creating images with bokeh.

Bokeh is generally round, because that’s the shape of the hole (lens aperture) inside your lens.
Aperture is controlled by a series of blades within the lens that come together to close the hole and move apart to open it. More blades equals a rounder hole. When you see hexagonal shaped bokeh, it’s because the lens used had fewer blades for closing the hole. Older lenses have more blades as les blades became the norm with auto-apertures due to speed of the automatic systems.

Aperture Shape.

Typically, when closing, the diaphragm cannot remain as round as when fully open. This is due to the number of aperture blades. With closed apertures, instead of discs (circles, circles), polygonal figures appear in the blur zone.

You don’t have to stick with the bokeh shape your lens creates!

If you want interesting bokeh shapes, you can buy bokeh filters to fit to the end of your lens. Just make sure you buy a size that fits the diameter of your lens. You can also create your own shapes to fit on the front of the lens.

Focus Distance

The closer the focuser position is to the MDF (minimum focusing distance), the stronger the blur will be. Therefore, even with a “dark” lens, you can get good blur by shooting close-ups when the lens is in focus as close as possible.

The distance between the lens and the main subject, and the main subject and the background has a big impact on bokeh.

To blur the background of an image using distance, the background needs to be at least two times further away from your subject than the lens is. So, if the lens is 0.5 meter from the main subject, the background must be 1 meters or more behind the subject. The further away the main subject is from the background, the more out of focus, or blurred, the background will be.

Optical Lens Design

The optics forms an unusual pattern for each lens separately. Personally, I consider the Sonnar design to have excellent bokeh. But now there are many other good lenses with incomprehensible multi-lens designs and nice bokeh. Optical design of some lenses even have a Defocus Image Control. Some photographers even turn the front element of the lens around to gain extreme swirly bokeh.

Composition.

Simply, with the same lens for the same composition (frame composition) with a different matrix size such as the image crop of the camera, will cause a different focusing distance, therefore, the intensity of the blur will be higher.

Background and Foreground.

It is very important that there is an understanding that the blur pattern depends on what will blur. Bright single light sources usually turn into luminous discs, and a uniform background into soft plastic porridge. The distance of the background and foreground also alters the Bokeh, it is all part of the creative process during composition. In the sample images I have used reflections from leaves, the river and the sun gaps in trees to get the bokeh I want. Rippling water with highlights of sunshine bouncing off the surface make great bokeh. Every one of those highlights will add to the bokeh effect if the water is out of focus.

It is a real art to make the bokeh part of the creative composition rather than a distraction.

Out of focus lights in the background of an image can create beautiful bokeh lights, so any dusk or nighttime scene with lights is perfect. You can try it out with distant city lights or fairground lights. In fact, any lights that are small, numerous, far away and out of focus are perfect for bokeh lights photography.

As stated before a lovely sunny day is also perfect for creating bokeh images. Leafy trees with the sun shining through from behind make a fantastic bokeh background.

Water droplets on glass make great bokeh too when out of focus as they pick up and reflect light.

Tinfoil that has been crumpled and straightened out a bit will reflect light in many directions. When the tinfoil is out of focus this it will create great bokeh as will Christmas tinsel.

Summary

So photographers often deliberately use a shallow focus technique to create images with prominent out-of-focus regions, accentuating the lens's bokeh and separating the main image from its background. Next time you watch a film on the TV or cinema look out for how this is used creatively in film too.

This is why I enjoy using vintage lenses alongside modern ones as they all give a very different bokeh. Explore the images on this site and see if you can spot different type of Bokeh.

Some folks add bokeh in post processing in software. For me this never works and actually destroys the fun of the creative process of photography.

See also "Why does the aperture not cause vignetting when it gets smaller?" in the Aperture section HERE

Video on the history of Bokeh

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Steve Cushing Impresionist Fine Art Photography

Embracing imperfection, recording emotions, one impression at a time…