The Zone System was created by worldwide accredited photographer Ansel Adams. It’s a scale which goes from ‘absolute black’ at 0% to ‘absolute white’ at 100%. He believed that it is important for there to be the whole tonal range in a photograph.
The centre of the spectrum is ‘mid grey’ at 50% which is what light meters will read when used so that the object/area the photograph is going to be centred around will be perfectly exposed.
For example, in this photograph below, the light meter was set so that the light box behind the object would be at ‘mid grey’ therefore anything darker than that would be photographed considerably darker although our eyes adjust differently.
However, in the one below here, the light meter recorded absolute zero as the subject’s face so therefore anything lighter than this will appear considerably lighter, but the subject is well exposed.
A light meter can be costly, but a must have tool for precise, keen photographers whom want to light their photographs accordingly.
A light meter only needs to have the ISO altered.
ISO is the sensitivity of film, or the sensor in DLSRs-
The higher the ISO the more light can be detected; therefore night shots are made easier to shoot. However, the higher the ISO the more grain the photograph will get.
The light meter will show the correct Aperture and Shutter Speed:
The Aperture is the size of the hole in which the camera will take the photograph:
F4 is a big hole so that more light can get in; this means that a faster shutter can be used. Also, lower F-stops mean that there is a shallow depth of field; whatever is in focus, everything around it will be incredibly out of focus and blurry.
F16 is a smaller hole, letting less light in and thus will need a slower shutter speed; however, the depth of field is greater so more of the depth of the photograph such as in landscape, more is in focus.
Shutter speed is the amount of time the aperture hole is exposed to light for. The faster the shutter, the less light is taken in. This can lead to over or under exposed images. Long shutters of slower than 1/125 can be liable to having motion blur if a camera is not on a tripod.
I hope this helps some of you who have asked for this. The best advice to give is to set your camera to manual and put things to the extreme to get a real hands on understanding!
All the best,