Understanding How Work Metering Digital SLR Camera (DSLR)

Every modern digital SLR cameras equipped with the manufacturer’s name Metering Mode, Exposure Metering, Camera Metering or for more practical we call Metering already assembled therein. In this article we will try to understand what it is metering? how it works as well as some major flaws that we must face (underexposed and overexposed). In the next article, further our understanding of the metering mode (matrix / evaluative, center weighted and spot metering).
What is Metering? What Purpose?
In principle, no different from the meter rolls used construction worker or meter tailor tape used to measure length, metering is only used by a DSLR camera to measure light, which is relatively more meticulous than the measured length.
Metering is used to measure the light that is seen by the camera (the light coming into the lens). When we see an object image through the camera viewfinder, light conditions in the object to be measured by the metering system. The main purpose of the camera metering system is to produce images that fit exposure. Metering done by analyzing the darkness bright picture of an object and then determine the amount of shutter speed, aperture and ISO so that the images you are right, not too dark or not too bright.
Her dizziness Hmm …. okay,imagine your eyes. When you feel the glare of what you do?  eyes instead! Unconsciously you reduce the amount of light entering the eye so that you are not blinded (not too bright). Conversely, when you feel the light is too dim automatically open your eyes wide.  eyes wide open so that eyes feel uncomfortable when I saw (the right exposure), as that is the task of the camera metering system.
How it Works Metering Systems Cameras & Weakness
When the camera sees the wall, metering systems will measure the light (dark light) is reflected by the wall (reflective). It is easy when all the images of objects reflect the same amount of light.
Fuss, each real world objects have different levels of reflection. When we photographed the sky, that perfect blue sky camera metering will simply calculate the exposure because there is only one light level to be calculated (blue). But when we take the sky with white clouds addition, metering must now count brightness and the brightness of the blue sky and white clouds should try to produce an optimal exposure. Now add the mountains and rows of trees into the object image above, the level of complexity facing increasingly complex metering.
How does the camera metering system designers anticipate this situation? The answer is to try to make the darkness light of the average of an object that any photo. Technically, the average dark light for the camera metering system is 18% gray (18% gray or gray normal) – not too dark and not too light – see photo below. An object image to the level of the reflected light with light dark complex will be “tamed” by the way.

These solutions generally is that we can use for normal shooting. But when we are faced with such conditions will be photographing friends’ faces with perfectly white background, the camera will make your friend’s face is darker because it must anticipate and take it towards the white background 18% gray alias underexposed. Or for example when you are photographing flowers in little glass cups are placed on a black tablecloth, the flowers in the picture will be much brighter than the original because it must carry the black tablecloth toward 18% gray alias overexposed.
How Should We Then?
Just as we can not continue to use auto exposure, to produce a good photo we can not use the camera metering system without some tricks (leaving the default position).