Bokeh. Possibly one of the most misunderstood, yet most bandied-about terms in the world of photography today – right up there with dynamic range, resolution, A-is-noisier-than-B and other such myths.
The term is a derivative of the Japanese word boke, which doesn’t really have a good translation into English. The closest we can get is ‘the nature/ character of blur’. It’s certainly not quantitative in any way – what constitutes good bokeh and what is bad or ugly bokeh is very much up to the viewer. There are some who like ‘busy’ bokeh where out of focus areas take on double images, swirls or other patterns; some like the pentagons and other shapes on highlights. Yet others prefer a uniform wall of gaussian blur foreground-background.
What factors affect bokeh? Mechanically, the lens design plays a big part. The nature of the optical formula and placement and design of the diaphragm, specifically. In general, round diaphragms produce the best bokeh; though having said that, the Leica 50/1.4 Summilux-M ASPH has some of the nicest bokeh around, but that has a strange multi-pointed star-shaped diaphragm. Telecentric lens designs generally have better bokeh than conventional spherical designs; this is because you’re less likely to get crossing of rays after and before the nodal point within the lens, causing double images and the like. It’s also why most of the new Nikon f1.4 lens designs have beautiful, non-offensive, smooth bokeh; they’re all telecentric designs and optimized for digital sensors.
One important concept to explain up front is depth of field. For a given aperture and focal length, a certain percentage of the focus distance will be in acceptable focus. This percentage doesn’t change with the focus distance; the difference is the longer the focus distance, the wider the actual, physical range that comes into focus.
The rules of optics also play a big part. The degree of blur is related to:
1. Real focal length (not effective 35mm focal length; longer focal lengths have shallower depths of field and thus more pronounced blur)
2. Aperture (wider apertures have shallower depths of field and thus more pronounced blur)
3. Distance between camera and subject (shorter subject distance means shallower depth of field – remember the percentage explained above).
4. Distance between subject and background (the further away your background from your subject, the more the blur).
With that, let’s look at two examples.
A. Worst case: subject is far away from the camera and close to the background; very short real focal length and moderate aperture. What will happen? Everything will be in focus. This scenario is precisely why compact cameras are incapable of delivering any noticeable blur under most conditions.
B. Best case: subject is close to the camera, with a distant background; long real focal length and fast aperture. This is your typical telephoto shot: beautiful isolation and no hint of foreground or background. It’s why you can shoot through light foliage or fences with a telephoto and not even notice their presence in the final image.
Good and bad bokeh, generally?
Remembering that it’s down to personal preferences, most individuals prefer:
1. Good gaussian defocus in background areas: uniform blur all over, with no double imaging
2. No color fringing on highlights, either left-right (lateral) or background-foreground (longitudinal).
3. Round highlights with uniform luminance, smooth edges and no internal pattern (those circles you sometimes see in out of focus areas are interference patterns caused by imperfect lens grinding or minute surface imperfections in moulded plastic elements)
4. Similarly smooth uniform blur in foreground out of focus areas. The foreground is something that few people look at or consider when addressing bokeh; it’s important because distracting foreground bokeh means that you can’t shoot through or around things. Nice foreground bokeh dramatically increases your composition options.
Which lenses do I think deliver good bokeh?
There may be some surprises in this list.
1. Any of the fast-aperture super telephotos.
2. The new Nikon f1.4 AFS lenses; 24, 35, 85.
3. The Nikon 105/2 DC and 135/2 DC.
4. Most of the Leica M ASPH lenses; specifically the 35/1.4 ASPH FLE, 50/1.4 ASPH, 50/0.95 ASPH, 90/2 APO ASPH. I don’t personally like the swirly bokeh of the older f1.0 Noctiluxes – caused by uncorrected spherical aberration.
5. The Zeiss ZF 85/1.4 Planar, ZF 35/2 Distagon.
6. Special mention to the Zeiss ZF 2/28 ‘hollywood’ Distagon – its curved plane of focus increases the apparent bokeh at the border and edge zones because the plane of focus is brought even closer to the camera than the central zone. It’s a pretty unique optical formula, and delivers spectacular results.
7. The Ricoh GR-Digital III – what, a compact? Yes. Used close up and wide open, the bokeh is up there with the best of them.
8. The Canon 85/1.2 L II
9. The Olympus ZD 45/1.8
Parting shot: Light is much more important than bokeh. You can always isolate a subject by the way it’s lit regardless of your lens and camera; you can’t do it if you’re using a telephoto lens as a crutch. What happens when you can’t get far away enough to get the whole subject in the frame? MT