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Over the past couple of You Connect tutorials we have had a look at the different ways that you can control the amount of light that enters your camera and strikes the film or sensor plane, the next step is knowing what level of light is correct for the image that you are trying to achieve, so this month we are going to look at methods of measuring light, and the contrast range within an image.

In photography, there are two ways that light can be measured. You can either measure the light is reflected from a subject, or the light that falls on the subject. These are referred to as reflected and incident light.

Measuring Incident Lighting
Because measuring incident light is measuring the amount of light that strikes the subject of your image, when you are measuring the incidental light you need to measure as close to the subject as possible, with the meter pointed towards the camera. A typical way of measuring incidental light is to use a separate meter with a light-sensitive white diffuser.

Related Downlaods

Incident light meter.pdf [PDF, 26 KB]

Measuring Reflected Light
When measuring the light that is reflected, the measuring device must be pointed towards the subject matter. This is the type of measurement that is generally performed by a camera. When measuring the reflected light, consideration is made of how much light there is, but also of the ‘reflection value’ of the subject. As different colours and surfaces may have different reflection values, many photographers use a ‘grey card’ to measure reflected light. A grey card has a reflection value of 18% that is considered to be an excellent standard value for a correct light measurement. The grey card is held as close as possible to the front of the subject, and the camera or other measuring device takes its reading from the card.

A neutral reflection value is important. If you have a situation where there is a black backdrop to your scene the camera will tend to overexpose. Similarly, and under exactly the same light level, if you have a white backdrop the camera will underexpose the image.

Related Downloads

Gray Card.pdf [PDF, 18 KB]
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