Today’s Question: When is it best to use spot metering versus matrix?
Tim’s Quick Answer: I think it is best to use spot metering when you have a sense of what the exposure needs to be for a specific area of the scene, especially in situations where you are concerned that the camera might be “tricked” by the scene using a different metering mode.
More Detail: My typical answer to this type of question about metering is that it really doesn’t matter which metering (or exposure) mode you use, provided you can achieve an accurate exposure relatively quickly and consistently.
When you use the spot metering mode you are telling the camera that you want to select a specific area of the scene to establish a meter reading from. That typically means evaluating somewhere around 2% of the scene you have framed up with your lens. Because of these issues, when you use spot metering you have the responsibility of pointing the lens at a specific area you want to establish your exposure based on.
With other metering modes such as evaluative or matrix, the camera is evaluating a larger area of the scene. Many cameras will also perform a bit of analysis of the scene the meter is evaluating, so that a more “intelligent” decision can be made about what the proper exposure settings should be.
Of course, the whole point of taking a meter reading is to establish settings for a good exposure. That might mean dialing in specific settings based on the meter reading when you are in the manual exposure mode. It might also mean adjusting the exposure compensation setting if you are in one of the semi-automatic exposure modes such as shutter priority or aperture priority.
Taking into account all of these considerations, to me spot metering is the best choice for situations where the camera may be “tricked” by the lighting situation, and you can achieve a proper exposure more quickly by metering off a small area of the scene. For example, when photographing the full moon at night, spot metering off the moon itself will generally get you a much more accurate exposure much more quickly compared to using other metering modes that will evaluate the entire scene and attempt to brighten up the dark sky.
If you aren’t comfortable using spot metering mode, using it can obviously be quite challenging, as it does require a bit more precision in terms of taking a meter reading, as well as a bit more knowledge of exposure. But there are many situations where spot metering can be faster and more accurate, so I think it is worth taking some time to get familiar with using spot metering for determining exposure settings.