THE EXPOSURE TRIANGLE

Photographers measure their light in Stops.

This comes from turning the dial on a camera’s shutter speed.

Traditionally, one turn of the dial equals one Stop of light.

Professional cameras are capable of greater sensitivity and can turn less than one stop.

Shutter Speed

This is the amount of time that the camera has to take the photograph.

With traditional Digital SLR cameras, this is the time that the shutter is exposed to the sensor to light. With newer mirrorless cameras or mobile phones there is not always a shutter, so it is the amount of time that data is captured from the sensor.

For constant lighting and natural light, a longer exposure (slower shutter speed) results in a brighter photograph.

For studio flash there is a limit to how fast most flash heads will fire, limiting the shutter speed to that of that particular flash unit.

Older flash units often have a limit of 1/60th of a second. Newer flash units commonly work at 1/200th of a second.

Newer flash units can often work much faster, up to 1/5,000th of a second. This High Speed Synchronisation uses a lot more battery power and takes longer to recharge between photos.

APERTURE


This is the diameter that the lens aperture is opened and is measured in F stops.
Three F-Stops equals one ‘Full’ Stop.

One turn of the aperture dial represents one third of a Stop.

With Traditional Digital SLR cameras the aperture can be opened and closed.

It’s important to note that:

  • A more open lens (e.g. F2.8) allows more light in.

  • A more closed (e.g. F22) lens allows less light in.

    With most professional lenses an aperture of F2.8 is the most it can open and F22 is as small it can go.

    Kit lenses (provided as a bundle with a camera) usually open to F5.6 and close to F22.

    Some prime lenses can open further to F1.2 allowing in a lot more light. These tend to be more expensive and are often designed for more niche uses.

    Assuming you leave the ISO and the Shutter Speed the same, then:

  • F2.8 will result in a brighter image

  • F22 will result in a darker image.

ISO

This is your camera’s sensitivity,
This used to be the sensitivity of the film that you put in your camera.

With film cameras an ISO of 100 would be considered ‘standard’, but with most new digital cameras, an ISO of 400-800 is considered a baseline standard.

With film, ISO 400 would have been used for overcast conditions & ISO 800 would be used for sports. ISO 1600 would have been for very low light or very fast sports.

The trade off with a higher sensitivity setting is increased grain within your photograph.
This was true for film and is still true for digital cameras.

However, newer cameras can go to very very high ISO settings and still produce very good results.

Some photographers will also deliberately use a high sensitivity setting to create a retro looking photograph directly from the camera, this can be particularly effective for black and white photography.
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This is also very effective for other genres of photography such as street photography, especially when some photographers prefer to have their grain directly from the camera, rather than adding it in during post production.