I've tried different types of metering for the same object shoot. But couldn't understand the metering exactly. Please explain the concept of metering in detail
Metering is just determining how much light is in the scene so you can set the right exposure values of shutter speed and aperture.
You camera has a built in meter to accomplish that. Many years ago the camera would just meter the entire frame to give you an average reading of the entire scene. Camera makers later introduced advanced metering patterns to try and make them more accurate.
The first was "Center Weighted" where more emphasis was given to the center of the image where you would expect the main subject to be.
Then came "Spot" metering of just a very small area so the user could pinpoint where to meter the subject.
Then finally came "Zone", "Evaluative", or "Matrix" metering where the camera uses complex programming to try and determine the optimum exposure value.
The confusion for many people comes from the fact that in many cases all these metering modes can produce the exact same exposure value. You may have to use a difficult subject in order to see any real differences. Try different metering modes on a strongly back lit or side lit subject for instance. Then you should see a difference.
It is always good to have choices and with experience you can figure out what metering mode works best for the type of photography you most do.
From a very basic perspective, the concept of metering is for your camera to measure the Reflected Light off your subject and determine the appropriate, Aperture/Shutter value and ISO speed.
If you give priority to any one of these and leave the other two as auto, or give priority to two and leave the third as auto, the meter will work out the second or third setting and provide you with a correct exposure.
The three common metering options offered by most cameras are, Evaluative, Centre Weighted and Spot Metering, and for a detailed answer on when to use each one, click this link
An alternative method for metering light, is to Meter for Incident Light, which is light hitting the subject directly - an explanation as to how it works is via this link
There are Two types of metering modes..
Mike covered Center, Matrix, or Spot. I prefer Center Weighted because my subject is normally in the center. Center sees an out of focus blob of light, and Weighted means the center (a circle perhaps half the height of your frame) is considered about 3x more important than the edges of the frame (called 75% weighted). Spot is a tiny spot, ignoring all else. Matrix sort of looks around in the frame more for unusually bright spots, which it takes into some consideration.
But all of those methods are reflective metering. The camera lens and meter sees the light reflected from the subject. If the subject is wearing black, or the background is dark, they don't reflect much light, so the meter reads low, so the metering attempts to correct it with overexposure. If the subject is wearing white, or in front of a white wall, the subject reflects a lot of light, and the meter reads high, and the metering tends to underexpose it. The goal of reflected metering is that everything should come out around the middle gray point. Sure, it could be a color, but a middle tone color. That is often about correct for average scenes composed of many colors and reflectances, but certainly there are special cases when it's not very correct (depending on the subject). Reflective metering is sort of an art, and we learn to adjust for the subject.
Beginners often do not realize that Spot metering is NOT more correct. It means that whatever the spot is should come out middle gray. Depending on the spot, that may or not be correct for the whole scene. And for example, you may not want faces to be middle gray. Spot metering requires some skill, knowledge and experience, and beginners are much better off with Center or Matrix.
Many handheld meters can do Incident metering, where the meter is NOT aimed at the subject, but instead, from the subject, the meter is aimed at the camera. This sees the direct light falling incident on the subject, and it meters the direct light itself. It is independent of how the colors of the subject can reflect light. This means that black things come out black and white things come out white (instead of gray). Accurate, little adjustment is necessary. But it is metered from the subjects position, NOT from the camera. It's very good for flash.