Shooting with a prime lens and zone-based manual is an almost Zen-like experience. No zoom to worry about. No panic as which focus points were selected or whether or not they happened to lock on to something completely random. The camera becomes a transparent tool that shoots as soon as you touch the shutter button.

There are many ways to set up zone focus, but I settled on a very simple rule-of-thumb. All I need to know is the focal length and roughly how much of the frame is being filled by the subject.

For example, when shooting with a 50mm lens I use the following settings:

That’s all I need to remember.

Usually I just set the camera to f11 and preset the distance based on the kind of framing I want. If I am struggling to maintain a fast enough shutter speed, I try a wider framing and reduce the aperture. With the 5D Mark III or Ricoh GR I sometimes also use “back-button” auto-focus to set the distance rather than relying on the lens markings (which are often small and difficult to read – even the Ricoh’s helpful DOF display on the LCD  is excessively miniaturised).

To help figure out these settings I wrote some software to tabulate the behaviour of different lenses for each desired subject framing (it does say “geek with camera” on the About page…).

Each table below corresponds to a particular framing. For example the table labeled “Full-Body (2.5m subject frame) in Landscape Orientation” lists the focus distance (i.e. how far away the subject must be) for each focal length lenses such that the vertical framing captures 2.5m (i.e. slightly more than a typical person standing up). The two numbers under the f-stop values correspond to the distance before and after the focal distance in which the subject will be still be reasonably sharp (using a circle of confusion of 0.029mm).

For example, if you want to shoot a person standing up using a 28mm lens, in landscape mode, you need be roughly 3m away. If you use f11 pretty much everything will be in focus. To do the same with a 50mm lens, stand about 5m away and use f16 or less to get the same depth of field.

There are two useful – if slightly obvious – observations from the tables.

• depth-of-field falls off much more rapidly in front of a subject than behind, so it is safer to err on the side of a focus setting that is slightly too close than too far
• wide-angle lenses really make it easier to get more in focus at wider apertures

One thing that I had not realised before is that using a wider-angle lens allows you to trade-off subject distance for aperture. So for example, if there is insufficient light to shoot at f11 with a 50mm lens, you could use f8 with a 35mm lens from a closer position and maintain the same depth-of-field. Whether or not this makes sense depends on how comfortable you are getting close and whether or not the resulting perspective distortion is a problem.

It is certainly the case that shooting moving subjects at close quarters is very difficult with a 50mm lens, as the combination of small apertures and high shutter speeds means that it is not uncommon to find hitting ISO 6400 or higher in the shady streets here.

The tables:

Head (0.5m subject frame) in Landscape Orientation

Half-Body (1.0m subject frame) in Landscape Orientation

Full-Body (2.5m subject frame) in Landscape Orientation

Group (5.0m subject frame) in Landscape Orientation

Head (0.5m subject frame) in Portrait Orientation

Half-Body (1.0m subject frame) in Portrait Orientation

Full-Body (2.5m subject frame) in Portrait Orientation

Group (5.0m subject frame) in Portrait Orientation