Shutter speed and aperture.
A short glossary on photography not to mix up things before going further.
– The shutter is a system that exposes the sensitive surface of the film or of the digital sensor as long as you want to. If you request an exposure of the film at only 1/15, the shutter gives access to the light during 1/15 of second (perfect to take pictures in the night). If you expose at 1/1000, the sensitive surface of the film or of the sensor will be exposed during a really short period (perfect for sport pictures).
– So the shutter speed is the time of exposure of a sensitive surface of the non-digital film or of the digital sensor. The larger is the time, the longer the light will affect the sensitive surface.
– The diaphragm is the mecanism that rules the quantity of light. If it is set to F4, it lets a lot of light entering in the camera. To give less access to the light, you will multiply by the root of 2, that is to say more or less 1.4. Thus, with a diaphragm set to F5 or F6, you will obtain a film or sensor two times less exposed to light.
Same quantity of light.
To obtain the same exposure of the sensitive surface, you can set differently the shutter speed and the aperture of the diaphragm. For example, to obtain the same quantity of light on the sensitive surface, you can close your diaphragm to increase the period of exposure. Conversely, you can open the diaphragm and reduce the period of exposure, the quantity of light will be the same. Why using two systems ? To easily increase or reduce the depth of field (Continuation of the article).
