Wednesday, January 23, 2013

Guessing the Light

Last weekend I was in Bath, taking photos of snow with a manual camera.

My light meter, like all in-camera light meters, measures reflected light (as opposed to incident light). It is calibrated to assume that all objects are midtone grey, i.e. reflect about 18% of incident light. This works fine in most situations, but when it meters an object that is unusually reflective (such as snow), it is fooled into thinking that there is a great deal more incident light than there actually is. Following the meter reading would therefore result in an underexposed image – grey snow. Taking photos of snow, or other scenes with unusually light or dark tones, thus involves an element of guesswork.

Saha and I often shoot with film, and because film is less forgiving and not all things are midtone grey, it helps not to be wholly reliant on the light meter. To develop a better sense of light (and also for fun), we sometimes play a game. One of us will point at, say, a wall, and call out a film speed and an aperture. For instance, “ISO 200 at f/8.” Then we both guess the shutter speed, and we check it against the light meter.

This photo is from the day Saha and I test-rode tokyobikes in Shoreditch: I over-exposed by one stop to get the right exposure for the light tones.

The label Sports has now been changed to Sports/Games.


Tommy said...

When Clinton was US President, press photographers noted that his hair had an albedo of about 0.18 and could thus be used in lieu of a gray card.

The Reluctant Rebel said...

@Tommy - That's awesome! A set of (long overdue) underexposed, overexposed and generally technically imperfect photos are coming your way.

@Sroyon - I find snow ridiculously difficult because you will, almost certainly, end up overexposing any moderately dark tones which may be in the picture.

little boxes said...

if rahul's blog wasnt enough, i now have this one to read and burn in envy.
and in my humble opinion, the over exposure works for this one.