The relationship and effect of aperture, shutter speed and ISO/ASA is one of the most crucial things to understand when learning photography. The ‘exposure triangle’ as it’s often refered to, can be at first difficult to understand, so we’ve created an easy ‘cheat sheet’ guide to help.
This ‘cheat sheet’ shows how a change in aperture, shutter speed, and/or ISO/ASA can darken or brighten (under or over expose) the image, as well as demonstrates the unique effect each setting has on the image, including depth of field, motion blur, and grain/noise.
Aperture (Depth of Field)
Aperture for example can broaden or shorten depth of field. As the aperture is closed down and becomes narrower depth of field increases, and the amount of light transmitted to the film plane/digital sensor decreases. Conversely a wider aperture (eg. f1.4) gives a shallower depth of field and allows more light to transmit to the film plane/digital sensor.
A wider aperture can create the effect of bokeh (an out of focus area) and is often used in portraiture. A narrower, more closed down, aperture tends to be used in instances where both the foreground and background need to be in focus, for example landscape photography.
Shutter Speed (Motion Blur)
Shutter speed on the other hand can freeze action, or create blur if there are moving subjects. The faster a shutter speed the less light that is transmitted to the film/digital sensor, with a shutter speed of 1/1000 capturing half the amount of light as 1/500 for example, or 1 stop of light.
Sharper shutter speeds tend to be used for wildlife and sports photography, where fast moving subjects need to be captured in a ‘freeze frame’. Conversely however slower shutter speeds can be used for intentional motion blur or long exposure photography.
The ISO/ASA of the film, or the ISO setting on a digital camera, dictates the amount of light recorded as well as the amount grain or noise which appears in the image.
A lower ISO/ASA (eg. ISO 50) will create a ‘cleaner’ less grainy/noisy image, as opposed to a high ISO/ASA (eg. ISO 12800) which will create a noisier image. As the ASA/ISO increases so does its ‘sensitivity’ to light, meaning for example that ISO400 will capture double the amount of light than ISO200, or 1 stop of light.
Balancing aperture, shutter speed, and ISO/ASA is crucial for obtaining correct exposure (ie. make the image not too dark or not too bright). Each of these settings however have different effects on the final image, resulting in changes of depth of field, grain/noise, sharpness, and blur.
If you want a copy of the ‘cheat sheet’ click here to download.