“In simple words ,Exposure is the amount of light captured in a picture when you click it ! “
Exposure in photography can be defined as the amount of light per unit area reaching your electronic image sensor for a particular frame/picture , as determined by shutter speed, lens aperture, and available light in the scene. Thus the exposure will change as below :
1.When the frame changes , exposure also changes.
2. When the shutter speed changes, exposure also changes.
3. When the aperture changes, exposure also changes.
To make a good picture we need to control the exposure so that the right amount of light is captured by your camera sensor. So when the exposure control is bad the picture can be too bright or too dark. Lets see how this is done.
Exposure control in Camera
The exposure is controlled in the camera by 3 factors :
1.Shutter
2.Aperture
3. ISO.
The first two factors Shutter and Aperture control the amount of light reaching your camera sensor, hence directly controls the exposure. The third factor ISO , by changing its values the picture brightness can be changed for a picture. When ISO is increased the light captured by the sensor is electronically boosted so as to simulate a brighter picture. So these 3 factors can be used to control the exposure. A combination of these three factors will get the right exposure for a particular frame. We can conclude the exposure control as below :
“In a particular frame/scene, a good Exposure can be achieved by having a particular combination of Shutter, Aperture and ISO values “
Let’s look at how the three factors affect the exposure for a particular scene:
- As shutter speed increases less light enters the camera and as shutter speed decreases more light enters the camera.
- As Aperture value increases less light enters the camera and as Aperture value decreases more light enters the camera.
- As ISO value increases picture becomes brighter and as ISO value decreases picture becomes less bright.
Below picture can give you a visual representation of the the three factors controlling the Exposure:
In exposure settings for a particular frame/scene, the Aperture , Shutter and ISO works such that when the value for one of them is changed it is required to adjust at least one of the other two so as to maintain the optimal exposure. This is generally termed as Exposure triangle, which is balancing the three settings, Aperture,Shutter speed and ISO , so as to obtain a good exposure. Read more about Exposure Triangle.
How to find Exposure change in a camera ?
All cameras have a light meter and it shows the meter reading in your viewfinder or LCD . The meter will show meter readings from -3 stops to +3 stops. Generally the 0 value is considered as the optimal exposure.
The balancing of exposure is done by referring to this meter. Ideally the aperture,shutter and ISO values are changed such that the light meter reading stays at 0.
The meter reading at 0 will give you an optimal exposure considering the amount of light in the scene does not change. The light meter reading also depends on the Metering mode set in the camera. For starting practicing exposure balancing Matrix metering / Average metering is recommended. Read Metering Modes for details on how metering methods work in digital cameras.