What is "Bokeh"?
Definition
When you use a lens at a wide aperture (ƒ1 - ƒ5.6), 'Bokeh' refers to the out of focus portions of the image - in particular its visually pleasing nature or lack thereof. Yes, it's YMMV and completely subjective!
Things to look for? An absence of "double-vertical" lines, perfectly circular highlights and a gentle gradation between the in-focus region and OOF parts.
From experience, Bokeh is more pleasing if there are a large enough number of lens diaphragm blades to form a circular (rather than pentagonal or hexagonal) aperture opening. Thus lenses with eight or more blades will usually give a more pleasing out-of-focus effect than those with only five. (N.B. This partially explains why Voigtländer 35mm, 50mm and 75mm LTM lenses feature ten diaphragm blades, whilst the 50mm Summilux-M has twelve.)
Alongside this, the lens optical design also has an effect, in particular how it corrects for spherical aberation in the forward and rear out of focus regions.
Links & Articles
The following URLs explore these issues to the nth degree:
- <vanwalree.com/optics/bokeh.html>
- <medfmt.8k.com/mf/bokeh.html>
- <pathcom.com/~vhchan/bokeh.html>
- <kenrockwell.com/tech/bokeh.htm>
- <luminous-landscape.com/essays/bokeh.htm>
<flarg.com/bokeh.html> is worth a peak in that it has an interactive JavaScript image-map, which allows you play around with bokeh effects.
For the technically minded, there is also an excellent article written by Harold M. Merklinger and published in Photo Techniques, May/June 1997. It's available online in Adobe PDF format and can be downloaded from the following URL (340 KB):
A note about possible broken links
This FAQ has over 900 external links. Over time it is inevitable some of them will break. If you are bothered by this, see this detailed topic elsewhere in the FAQ.