Exposure is the amount of light that comes into the camera to create the photograph.

It is made up of three components:

  1. ISO-Sensitivity to light.


2. Shutter Speed-the length of time that the camera’s shutter is open during the exposure..
For more on shutter speed. 

3. Aperture-how wide the cameras lens opens to allow the light to come in.

For more on Aperture.


How Shutter Speed, Aperture, and ISO work together


Measuring Exposure

Stop is a term used to measure the amount of light in an exposure whether it comes from the shutter speed, the aperture or the ISO.  Adding a full stop of light doubles the amount of light reaching the sensor. Reducing the exposure by a stop halves the amount of light reaching the sensor.

Through the Lens Metering

The meter in your camera is a reflected-light meter.

A reflected light meter averages the tones in the scene and selects the aperture and shutter speed values that will make the whole scene medium gray.

Metering Modes:

Evaluative or Matrix metering-default mode in most cameras. It considers the whole frame, dividing it into zones and comparing to a database of similar tonalities, selects the exposure.

Spot Metering-only evaluates the light around the focus point.

Center-weighted-evaluates the light in the center area only.

Exposure Compensation-a way to force the camera to make an exposure either lighter or darker than the meter reading. Good for backlight, extremes of light and dark or when scene does not average out to medium gray-such as a snow scene or a night scene or a scene in deep shadow, and when the scene includes a considerable amount of sky.