Eli5 What Is Bokeh

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Photography Bokeh (Answered)

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In: Technology

Bokeh has to do with shortening your depth of field, when you apply a bokeh, you get an affect that makes everything outside of a very specific range out of focus. So like in a portrait, the subject would be in focus but the surrounding would not be. You notice it more in photos that have a lot of discrete highlights in the background, like a city at night, or dappled sunlight through leaves.

Bokeh is a side effect of lens geometry. A lens, in any system, has a limited depth of distance where the image is sharply focused. Outside that range, the image is blurred. But, blurred isn’t always bad. In many artistic photographs, the photographer’s choices for focus make an important contribution to the overall look of the image.

In other applications, particularly moving imagery or scenes containing bright light sources at night, some optical effects caused by lens bokeh are unavoidable. For example, when there is a near focus field, to capture an image of something near the camera, and a bright source, like a distant plane light at night, the “out of focus” airplane light can appear distractingly large in the image. This can be further complicated by cameras with few aperture blades, causing the out of focus blob to have as few as 3 distinct “sides”. This gives a “big triangle” in the picture which wasn’t seen by the photographer’s eye. So while it’s arty in some images, it’s ugly in others.

Bokeh is the name for the aesthetic quality of an out of focus part of the image. That’s much easier seen than explained.

[Here’s a random normal photo](https://www.adorama.com/alc/wp-content/uploads/2017/06/1-shutterstock_588634790.jpg). See the blurry background. That’s the normal kind you see everywhere.

[Here’s swirly bokeh](https://i.pinimg.com/originals/99/0b/09/990b097b201bc8bd810b2d3ed4911eff.jpg). This is caused by lenses with a particular kind of defect, that some photographers like anyway.

[Here’s donut bokeh](https://t3.ftcdn.net/jpg/03/53/50/04/360_F_353500437_drGyzDDKemhG7uCmNYqHsb1pqkOWlsPF.jpg). Generally seen as very unappealing, this is caused by [catadioptric lenses](https://en.wikipedia.org/wiki/Catadioptric_system) (more or less a telescope bolted to a camera)

[Here’s heart bokeh](https://picjumbo.com/wp-content/uploads/abstract-bokeh-hearts-real-light.jpg) caused by a shaped insert in the lens.

In general most discussion will be regarding the first kind — that’s the standard kind of blur you see, but there’s still minor differences between lenses and some sorts are more or less pleasing.

Thanks everyone for all the info and replies, this question has been answered.