Artefacts of Light

This is the first post in a new series of blog posts about different aspects of photography, called Artefacts of Light. In this series, I want to explore technical details of photography in a way that non-photographers can easily understand and apply to their own photos.

The subject this time is a particularly beautiful artefact called Bokeh (the name comes from the Japanese word Boke for blur or haze). I‘m sure you have seen it before, but it‘s one of these things that you start to appreciate a lot more once you have a name for it. It refers to the rendering of out of focus lights, when the light source appears a lot bigger on the photo than it actually is. Like this:

If everything in this photo were in focus, the light sources in the background would be small dots. But because they are out of focus, they become these big, beautiful dashes of light.

The size of Bokeh depends on several factors, the most important being a shallow depth of field — i.e. a very narrow band of the scenery being in focus and big parts of it being out of focus. Depth of field is lower when using cameras with big sensors like DSLRs and „fast“ lenses with the aperture wide open. It is therefore a lot harder to get nice Bokeh with compact cameras.

Bokeh is most easily visible in photos made at night with light sources visible in the background. While Bokeh still happens in bright scenes as well, the light from the background tends to bleed together, an effect sometimes called Light Bloom, as in this photo:

I love the effect Bokeh has on night time/evening portraits, so I often try to get some out of focus light sources in the back. Its fun to experiment with different sizes of Bokeh by opening/closing the aperture or using a longer focal lenght (i.e. using a telephoto lens instead of a wide angle). Here is a photo where the aperture was closed down to get smaller Bokeh:

The shape of Bokeh depends on the layout of the aperture diaphragm of a lens. One of the lenses we used a lot in the beginning, the Canon 50mm 1.8, uses 5 blades for it‘s aperture, which is why the Bokeh has a pentagonal shape with this lens:	The faster version of the 50mm we use now, the Canon 50mm 1.4 uses 8 blades and has a much more circular, octagonal shape:

Some photographers swear by lenses with more blades or other mechanisms so that all Bokeh are perfectly circular but I am quite fond of pentagonal or octagonal ones. Still, circular Bokeh sure is beautiful as well:

That's it for this time, I hope you enjoyed this post, and I'm always happy about feedback!