In order for the camera to know what the proper exposure setting should be, it has top measure how much light is coming in to the camera.
A metering mode is a specific pattern of measurement used in this calculation. It is an actual shape of the view finder. The first and most common shape is the evaluative which measures light from the entire scene as seen in pink here.
The spot mode is different and that it only measures light in the very center part of the view finder.
You should be asking your self a question is this important. Well, if very bright lights are in the pattern of the metering mode, they will be included into the calculation of the recommended exposure settings. The typical result of this is that midtones will be underexposed. In plane language, this means your pictures are going to be darker when you have very bright lights in your metering zone. As an example of this candle, I took a picture of this candle, using the spot metering mode and I made sure the candle was in the metering pattern.
Now, if bright lights fall outside of the metering zone as in the second example, they will be ignored by the cameras metering system and the result will be brighter midtones and slightly blown out highlights. This can be very useful when you are shooting into backlight.
The partial metering mode is similar to spot mode, but it measures nine percent of the center instead of three percent. And lastly, the center weighted metering mode is a combination of the partial and evaluative metering modes.
Now, metering modes are confusing for beginning photographers, so please do not get frustrated. Just remember your camera is calculating light based on specific shape patterns and these patterns along with light conditions you are shooting in will affect the automatic exposure settings of your photographs.
What I recommend for beginners is to just stick the evaluative and spot metering modes because their patterns are easy to remember and they are pretty easy to predict and they are really easy to adjust.
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