Tuesday, April 19, 2011

Hyperfocal shots

Photography requires dealing with four variables at the same time. The amount of light (or exposure) is controlled by how long do we let light into the camera (shutter speed) and how wide is the hole used to do it (aperture or f-number). ISO speed (or film speed) controls how sensitive does the photosensitive element (sensor or film) respond to light. Focus (and its cousin depth of field) decide which parts of the picture are rendered sharp and which are not.

hyperfocal selfie
(Kodak Retinette IA, Fuji Neopan 400, EI 400/27°)

The photographer lives in this four-dimensional space and must find a point (that means, set values for each one of these variables) in order to make a photograph. Throughout the development of photographic cameras, clever systems have been devised to take care of these decisions automatically: shutter priority, aperture priority or full automatic exposure programs, automatic ISO setting, autofocus, ...

Nevertheless, focus remains a crucial aspect of photography because the photographer still has to decide what distance to focus to. Autofocus systems are only able to turn the focus ring very precisely real fast (*).

One way to forget about focus at once is to take advantage of an optical trick. For a given aperture, set focus to a distance that lets the far end of the depth of field on the infinity (**). This is the hyperfocal distance H corresponding to that aperture. Everything from H/2 to the infinity is in focus now.

hyperfocal asia market
(Kodak Retinette IA, Fuji Neopan 400, EI 400/27°)

The hyperfocal distance is very useful when I do street photography or when I take photographs from the chest, with the camera hanging from its neck strap, because I just need to mind about the near end of my depth of field. I try to estimate the distance to my subjects so that I take their picture when they are farther away.

Letting the hyperfocal trick take care of focus gives the photographer the ability to shoot really quickly, or the freedom to concentrate about other photographic aspects.

(EOS 40D, EF 24mm f/2.8, 1/400, f/11)
(for this shot I knew that everything between 0.8m and infinity was going to be sharp, so I was able to worry exclusively about the composition...)

(*) At least it should be this way. I know that modern cameras can decide which one of the autofocus points to set focus on as well, but... what decision remains for the photographer, then? :-/

(**) A depth of field scale on the lens comes in handy for this setting.

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