Understanding Exposure - Part 1: Exposure Triangle

Photography has so many technical terms and jargon that it can all get so confusing at times. One thing that any photographer should fully understand, though, is exposure. Photography means ‘capturing the light’ and exposure is the total amount of light that reaches the film (traditional photography) or sensor (digital photography).

Exposure is defined by three elements which make up the ‘exposure triangle’. These would be ISO, aperture and shutter speed. These are all connected to each other and by adjusting any of these settings, you must keep the other two in mind.Although we will be discussing these settings in more detail in future articles, let me give you an overview of how they work:

Shutter speed - it is the length of time that the camera’s shutter remains open. The longer you keep the shutter open, more light is let in. The sensor also takes a longer time to capture the subject which means there is a bigger chance of getting blurred shots with long shutter speeds. Of course, blurring your shot deliberately to achieve an effect is one of the tricks you can do by playing with shutter speed. Shutter speed is measured by time in terms of seconds or fractions of seconds. ‘1’ would be one second while 1/1000 would be a thousandth of a second.

Aperture – this is the diameter of the camera lens opening where light travels through and reaches the image sensor (or film). The combination of shutter speed and aperture size regulates the sensor’s degree of exposure to light. Aperture is measured in ‘f-stops’, which is the ratio of focal length to aperture diameter size. The larger the diameter, the smaller the f-stop number, and vice versa. Therefore an f/2.8 f-stop would have a larger lens opening compared to an f/8.

ISO (International Organization of Standardization) – in film photography, it is the sensitivity of film to light and it is also referred to as ASA. In digital photography, it is the sensitivity of the camera sensor to light. Although the mediums may be different, the principle is still the same. ISO is measured in numbers such as 100, 200, 400 and 800 and the lower the number, the less the sensitivity and therefore, the finer the grain of the image.

You might wonder what would be the perfect exposure for your shots. ‘Perfect’ would mean you have achieved your desired effect, which varies from one image to another. The lighting conditions will be different in most outdoor shots so all three elements have to be adjusted accordingly. Studio shots, however, make use of controlled lighting which lessens constant settings adjustments.

If the exposure triangle is not set properly to balance the amount of light, two results can happen to the image. Overexposure occurs when too much light is captured and the details’ highlights become all white (commonly called ‘blown out). Underexposure happens when too little light reaches the image sensor and there is no more shadow detail. Dark areas appear pitch black instead. In both cases, there is loss of detail. This is not necessarily a bad thing if this is the intended effect of the photographer.

Since exposure in photography is such an expansive subject, this article has been divided into two parts. Stay tuned for Part 2 which will provide more exposure information such as using the light meter and the difference between auto and manual modes.