Friday, November 7, 2008

Is My Lens Bokeh?

I recently replied to a question on a photography community site about "What lens do you like for good Bokeh?" My reply prompted a ton of discussion about what Bokeh is.

Many photographers had posted sample photos of their lenses that apparently showed Bokeh. Some photos showed nothing more than a subject in the foreground and a blurry background with the slightest of variation. A few even had completely solid single color backgrounds that were blurred out where you could not even see what I call Bokeh.

I argued that these photos did not show Bokeh well and thus the lenses could not properly be judged. The solid lines with high contrast that will display Bokeh properly were not there. How could you judge a solid blurry green background as having a lens that softly and evenly blurs. Even the worst of lenses on a solid background would give you nice soft even tones.

Other photos showed what I thought were good examples such as this great photo from Robert Gulotta "Wine Glasses" (Posted with permission).

Robert_Gulotta_Wine_Glasses
Robert Gulotta "Wine Glasses" - www.momentsphotographers.com

The bright circular spots or sparkles that have sharp contrasting edges can display Bokeh much better. Here if you look at the lower left hand side, the dark black area shows a nice soft transition as you move up and to the right without any distortion. This shows a lens with great Bokeh.

In this next photo by Matthew Brennan "Purple Iris" (Posted with permission), the Bokeh is still rather good but the spots are not as soft and the shapes are irregular. This odd shape is caused by a non round lens iris. Usually these shapes are caused by irises that use very few straight blades. Some irises will use more blades to keep the opening round and others will curve the shape of the iris blades to help create a round opening.

Matthew_Brennan_Purple_Iris
Matthew Brennan "Purple Iris"

The spots themselves are cause by a light source that is smaller than the lens opening itself. All sorts of small light sources from pin point reflections, small light bulbs and even a thin line high contrast hard edge of a blade of grass will cause Bokeh. The larger the opening or aperture, the larger and softer the spots will be. So typically, a very fast lens with an aperture of f/2.0 or f/2.8 will have a larger opening and better Bokeh than an f/3.5 or f/4.0 lens.

Some guidelines for what will create Bokeh keeping in mind that all lenses will create it.

- Larger Apertures
- Larger Front Lens Elements
- Aspherical Lenses more than Spherical Lenses
- Diffractive Optics Lenses more than Aspherical Lenses
- Shorter Lens to Subject Distances
- Greater Subject to Background Distances
- Smaller or Sharper Background Light Sources from Lights, Reflections or High Contrast Subjects

All lenses will create this Bokeh effect, some more than others. And although it may look good and interesting at first glance, generally it only becomes distracting and undesirable. There are a few exceptions, wine glasses at a wedding are a good example.

The discussions on the sites turned into a "What is Bokeh?" discussion. Some professionals agreed with what I had to say and yet other professionals suggested it was only the blur. Which is it?

Now that I have shown you what I think Bokeh is, I will share with you the 'literal' Japanese translation, the 'literal' definition of the word Bokeh, and the 'intended' use of the word Bokeh.

The word Bokeh, pronounced bo k-eh, as in BO and Ke in Kenneth, comes from the Japanese word 'boke' (ぼけ) meaning "blur". But, then that is a very literal definitions as the Japanese word can also mean 'dull', 'not sharp', 'faded' and even 'dim witted'. This is the translation to the word boke, not Bokeh.

So now that we know the word means 'blur' should we assume that Bokeh refers only to the blurry parts of a photo? The answer is NO. We can say this for two reasons. One is that the word 'Boke" means 'blur', which is the root of the word Bokeh. Bokeh was a word that was developed specifically for photography to describe; 'the aesthetic quality of blur in photography' or 'the way a lens renders the out-of-focus or blurry objects'. These are two of many similar descriptions found in many photography magazines, books and well respected web sites.

Note the second part here, how it renders out-of-focus areas, and not 'is the out of focus areas'. So, the soft blurring of out focus areas are just that, blur, or out of focus. The Bokeh, is how the blur renders objects. As per my discussion above, this is best shown with light sources or smaller high contrast objects.

So there you have it, you can now decide what you think Bokeh is. Different lenses will have different Bokeh based on three factors, the aperture, the quality of the lens including the iris, and the actual lens design or rather optics of the lens. For example, Diffractive Optics Lenses tend to give much better magnification with smaller and lighter lenses. But, the optics design of these lenses usually cause bad Bokeh and even exaggerated Bokeh that will show up where other lenses would not show Bokeh.

For a little more on this, you can check out this .PDF file of Bokeh ratings on various lenses. It is somewhat subjective but a good read.

Lens Bokeh Ratings by Mike Johnston

© 2008 Francois Cleroux

(Version 1.00 - November 2008)

Please feel free to leave comments, corrections, ideas, thoughts or suggestions.

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I value thoughtful comments and suggestions. If you like or dislike this post, please let me know. If you have any ideas or suggestion, comments or corrections (I do make mistakes) please also let me know. Thanks.

- Francois Cleroux