In photography, Metering is a method to calculate the optimal exposure from the light source for the subject you are shooting at. Back in old days, photographers used to rely on an external light metering device because cameras were not equipped with the sensor that can measure the sensitivity of the light and give you the information about the exposure settings. But today, every modern DSLR cameras come with the sensor that meters the light entering the camera sensor and determines the correct exposure settings for you. Even though some DSLR brands use different naming convention for the metering mode, overall idea of the metering system is same. In this article, I will be taking a reference of Nikon D90 to explain different metering modes available in modern DSLRs but this technique implies to all the DSLR models.
What is the Metering mode?
Metering mode is a different exposure mode available in your camera settings. Metering mode is used to deal with correct exposure for the subject. It is mainly used when there is a challenging lighting condition (too dark or too bright or the combination of both).
When you frame your subject, it determines the intensity of the light coming into the sensor and give that information to the light meter. Most of the time camera does a good job sensing the light but sometimes it gets deceived by the light source when there is a mixture of the dark and the bright light source. If you are shooting in Auto mode, camera tries to set the correct exposure automatically by calculating the correct combination of the shutter speed and an aperture value (F-stop) and different other parameters which we will discuss later in this article. Like I said before, it works perfect most of the time unless there is a serious lighting condition, sunset with the dark sky and the bright horizon or the subject under the very bright sunlight, for example.
If you have got the idea of what is Metering and when to use it, lets talk about the different types of the Metering modes available in the modern DSLRs.
There are three common Metering Modes available in almost every DSLR and they are :
1. Matrix Metering
Nikon D90 uses different Matrix metering depending up on the type of the lens you are using. It uses 3D Color matrix metering II with type G and D lenses and Color matrix metering II with other types of CPU lenses. This is the default setting for the D90. When you look at the LCD screen on the top of the D90 body (on the right side where the shutter release button is), the Matrix metering mode is indicated by the black rectangle shape with the dot in the middle.
While metering using Matrix metering mode, camera divides the entire frame into multiple zones and calculate the exposure based up on the colors of light, distance of the subject, color tones etc. Camera collects the information from all the zones but gives the priority on that area where your lens focus point is on (inside the frame). Matrix metering mode does pretty good job most of the time and should be used for day to day photography.
2. Center-Weighted Metering
Center-Weighted metering mode is represented by the little circle with a central dot inside. Like in the Matrix metering mode, it also calculates the exposure from the entire frame but the center area is given more priority (weight) during the calculation. As per Nikon website, It gives weight of 75% to 6, 8, or 10-mm circle in the center of the frame. As name suggests, Center-Weighted metering mode doesn't rely on your focused area but gives the priority to the center of the frame instead. It is not recommended setting for most of the time and also considered as a least accurate metering method to use because your subject might not be in the center all the time. It should only be used when you want to emphasize the center of the frame.
3. Spot Metering
Inside the LCD screen, Spot metering mode is indicated by little circular dot. Unlike other two methods, while metering light, it only gives priority on a small area where your focus point is and ignores everything else inside the frame. As per Nikon website, it meters 3.5mm circle (about 2% of the frame) centered on the active focus area. It is widely used when you want to give proper exposure to your focused area no matter how the surrounding will be.
How to change the Metering mode?
It depends on camera brand and model but in Nikon D90, there is a dedicated button left to the shutter release button. When you press that button and rotate the rear command dial, it switches the metering mode from one to another.