Image exposure

In order for an image to form on a photographic film or digital sensor, the area needs to be exposed by an amount of light corresponding to the sensitivity (or gain) setting. We therefore need to understand how to calibrate the camera to best suit the available light.

Examples


			Larger view
1000 lux: Sensitivity / Noise level High Image 1: Good exposure with frozen action. Note: Distance to roundabout 40 meters, speed of car 40 km/h (25 mph).

Sunshine – Since lots of light is available, the camera will choose a small iris opening and a fast shutter action, allowing maximum image quality in reference to great depth of field and clear frozen action. Lots of light offers the potential for high image quality.

Overcast – You need to prioritize. If depth of field is a priority, reduce the shutter speed. The alternative is to maintain fast shutter action, freezing moving objects and reducing the depth of field.

Evening and night – As we run into lower light situations, the camera will need to adjust the sensitivity in order to make use of the available light. As the sensitivity improves, interference (noise) appears in the image area. Noise will be seen as grainy particles in open skies etc. Increasing the sensitivity will raise the noise level.

	Sunshine	Low light setting 1	Low light setting 2
Shutter speed	High	Low	High
Lens opening (f stop)	Small	Small	Large
Gain	Limited	Limited	Full
Image priority	All	Depth of field (DOF)	Movement
Result	Good DOF, Clear image, Frozen action	Good DOF, Clear image, Blurry movement	Limited DOF, Noise, Frozen action,