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UNDERSTANDING METERING MODES

Your DSLR camera has different metering modes. These metering modes affect how your camera reads the light in the scene and determines your exposure. Matrix or evaluative metering is going to give the best results by far in the vast majority of situations.

  • Matrix or evaluative - Recommended in most situations. Camera meters a wide area of the frame and sets exposure according to distribution of brightness, color, distance, and composition for natural results.
  • Center weighted average - Metering is weighted at the center of frame then averaged for the scene (approximately 20% of the frame)
  • Partial - Covers about 9% of the frame at the center
  • Spot - Camera meters an area centered on the selected focus point (approximately 1 - 3% of frame). Spot metering uses the center focus point if none is selected.
Here are some example images that illustrate the effect of the different metering modes. The ISO and aperture are constant in each image.

This image was shot using matrix metering and is a good exposure for the scene. The shutter speed is 1/640th in this image.

 

In this center weighted metering scenario the camera has given more importance to the browns in the very center of the frame causing the image to be somewhat over-exposed and too bright. The shutter speed in this photo is 1/400th.

 

In this spot metering scenario the camera has attempted to render the brown tone as a medium tone. Since the brown is actually a darker tone the image is over-exposed and too bright. The shutter speed in this image is 1/250th.

 

In this spot metering scenario the camera has attempted to render the bright white as a medium tone. Since the white is actually a much lighter tone the image is under-exposed and too dark. The shutter speed in this image is 1/2000th which is 3 full stops difference from the image above.
This is 18% medium gray. Your cameras metering system is trying to render the tone you are metering as medium gray. So, if the tone you are spot metering is lighter or darker than medium gray the image will not be correctly exposed.

Compare this gray to the two spot metered images above. The camera really does a good job of placing the spot metered tone as a midtone value. The problem is that those tones are not midtones. They should be darker or lighter which is why matrix metering works the best for this scene.


 

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