Bokeh Rant

We all know that the term “Bokeh” refers to the rendering of out of focus areas of an image. Mr. Johnston claims credit for the Americanized spelling and this term has been increasingly used since the millennium. Before this time, though there were some references to this quality of a lens, very few photographers showed deep interest in it. But recently I have noticed that this is now a rage in various forums and lens tests.

I have used a range of lenses from primes to zooms and manual focus to autofocus lenses. I have used Planars, Tessars, Sonnars among others. I have used lenses from the 1950s to the latest nano coated versions. I also love to look at photographs. I love to analyze the photographs especially in the context of the lens used to capture it and more so if the aperture is wide open. Usually prime lenses have a signature and sometimes it is possible to identify the lens used, case in example, Leica Noctilux wide open. The bokeh is an important aspect of lens rendering and its signature. But it is not the only parameter of a lens.

My concern is that the photographic community’s recent overtures to this single characteristic of a lens has gone to a state of obsession. There is also lot of misconception about bokeh especially the idea that the more blurred the background the better the lens.

My take on this.

Bokeh is determined by the spherical aberrations of a lens. All lenses have some spherical aberration. A good lens will have less of it. But this is over simplification and completely erroneous if you believe this is the only parameter which determines Bokeh. Any bright point in the out of focus area is going to be a disc. Whether the edges of this disc appear bright or is smooth is determined by the spherical aberration. So spherical aberration primarily determines the edges of point source of light in out of focus area. It has very little role in the transition characteristics of the in-focus and out of focus areas or the rendering of points which are not bright in the out of focus areas.

Factors which really Affect Bokeh

1. The most important determinant of bokeh is the focal length of the lens. The longer the focal length, the smoother the bokeh. (You can see this easily even in a zoom lens where the bokeh at the long end of the zoom is smoother compared to the bokeh at the wide end.) If you simply want a smooth bokeh use a telephoto lens you will be happy for the most part. But there are exceptions as there are other factors which play a role in bokeh. (Please note I have used the term “smoother” and not “better”). There are also other factors that affect bokeh.

2. The aperture of a lens is another important determinant of bokeh. The character of bokeh of the same lens changes with the aperture. Some lenses have good bokeh wide open, some stopped down a bit. If ever there is a generalization then the sweet spot of any lens for bokeh appears to be f/2 (in 35mm format). I have observed the following

1. An f/2 lens will have a better bokeh than a f/1.4 (or wider) lens even if the lenses made by the same manufacturer.
2. Even if a lens has a maximum aperture of f/1.2 or f/1.4 (or any other below f/2), the lens will have its best bokeh at f/2.

3. Next Bokeh is affected by lens design. A sonnar based design is going to have a better bokeh compared to a double gauss planar based design. I am a big fan of Sonnars. They are the best designs for portrait lenses.

Factors which do not significantly affect the Bokeh quality.

1. Contrary to popular belief the number of aperture blades do not significantly affect bokeh. But lens design does.

2. Zoom lenses do not necessarily mean bad bokeh and primes do not necessarily mean good bokeh.

Finally bokeh rendering of the same lens with the same camera changes with different background conditions and bokeh is very subjective so what works for one photographer may nor for another. A good bokeh for fashion portraits is not necessarily a good one for news or sports coverage.

As far as I know there are only 2 lenses designed give photographers the option of changing the bokeh rendering. These are the Nikon 105mm and 135mm DC versions. These lenses are unfortunately difficult to use and suffer from bad reviews from users who did not use it as it is intended. I have the 105mm DC Nikkor and as far as bokeh is concerned this lens represents the pinnacle of lens design.

A Gaussian blur like effect is the most sought after by many photographers but it is not the best. It may work occasionally for some portraits but it has nothing to with creating a dimensional (3D) look. In fact, it does the opposite, it flattens the image. Heck if this diffuse Gaussian blur like bokeh is what you like then please do not waste your money. Buy any cheap lens and shoot. To get the Gaussian blur for the background buy this software. You will be happy and save a lot of money at the same time.

Finally a word about Dimensionality or 3D look. Yes you can get this look if you know how to get it.

1. You need a wide angle lens to get 3D look. You may be do with a standard or short telephoto but a lot depends on the subject. The best focal length is 35mm for this.

2. The bokeh is important for 3D in the sense that the lens should render the background with a slight blur where you see the background and identify elements in but should not distract the subject.

3. The most important aspect is your subject and composition. Without this nothing can compensate to produce a magical 3D like rendering.

It seems that much of the lens evaluations online including the forums concentrate too much on bokeh and whenever a photo is posted the comments are mostly about the bokeh. There are very few who show concern for the subject. Are we forgetting the picture for the background?

Your comments are most welcome.