One of the areas of confusion I see in questions from readers is about the difference between exposure modes and metering modes. It seems a lot of photographers mix them up, and may not even be aware of the difference.
Here’s an example of the sort of question I get:
“I’m not sure what you mean by Auto exposure as a setting. On my Nikon, exposure settings are under Metering, where I have three choices – matrix, center-weighted, or spot. But no Auto option there, and I can’t see any other exposure-related Auto options.”
If you already know the answer to this then great, you’re on the way to understanding how exposure works on your digital camera. But if you don’t, let’s dive in and look at the details.
What is a metering mode?
In the reader’s question above, center-weighted, spot, and matrix metering are all metering modes. Most digital cameras have at least two of these options and Canon EOS cameras have a fourth called partial metering.
The job of the metering mode is to determine how much light is coming through the lens and reaching the camera’s sensor. That’s it. The metering mode doesn’t decide which exposure settings (i.e. ISO, aperture, and shutter speed) to use. It just tells the camera how much light is coming through the lens.
Spot, center-weighted, and partial metering are all legacy metering modes. They exist on your camera not because they’re particularly useful, but because cameras have had them for decades. Center-weighted metering, for example, has been around for as long as I can remember. Matrix metering is newer and better, but it’s easier to leave center-weighted metering on a camera than take it off and reduce the features list.
Below you can see the type of scene that photographers used center-weighted metering mode for before matrix (like an overall average of the scene) was added to cameras.
The idea is that taking the exposure reading from the center of the frame reduces the likelihood that a bright sky will make the camera underexpose the photo. Now matrix metering will give you a more accurate result, especially if you include more sky in the composition.
What is matrix metering?
Matrix metering is Nikon’s name for its most advanced metering mode. To add to the confusion, other camera makers use different names for the same thing. Canon and Sigma call it evaluative metering, Sony and Pentax use multi-segment metering, Fujifilm’s is multi, and Olympus calls it digital ESP metering.
Regardless of the name, each of these exposure modes works in the same basic way. The camera divides the viewfinder into zones, each one taking a separate reading. The camera analyzes the amount of light hitting each zone and works with your selected exposure mode (see below) to calculate what it thinks is the correct exposure.
The overlay on the image below shows the evaluative metering pattern of the Canon EOS 80D. The viewfinder is divided into 63 zones for metering purposes (the metered area excludes the edges of the frame).
Evaluative metering is super useful when using E-TTL (electronic through the lens) portable flash units (aka speedlights) as it works with the flash to calculate the required exposure.
In my opinion, in today’s advanced digital cameras matrix / evaluative metering is the only metering mode you need. The rest are redundant.
What are exposure modes?
The exposure mode determines how the camera interprets the information given to it by the metering mode. The exposure mode’s job is to determine which ISO, aperture, and shutter speed settings will provide the best exposure, depending on the parameters set by you, the photographer.
If you’re using Aperture Priority mode, for example, with the aperture set to f/2.8 and the ISO to 400, then the camera knows its job is to select and set the shutter speed according to how much light is reaching the camera’s sensor. It really is as simple as that (a lot of sophisticated technology goes into that single calculation in an effort to get an accurate result).
Virtually every digital SLR or mirrorless camera has the following exposure modes:
- Full Auto (green icon usually)
- Programmed Auto (P)
- Aperture Priority (A or Av)
- Shutter Priority (S or Tv)
- Manual (M)
Below you can see the mode dial on a Nikon camera. The four most useful exposure modes (Manual, Aperture Priority, Shutter Priority, and Programmed Auto) are separated from the camera’s automatic exposure modes by a white line.
Again, the names may vary from one manufacturer to another. Programmed Auto is also called Program AE, Program Auto, Program Shooting, or Hyper-program. Shutter Priority mode is also called Tv or Time Value on Canon cameras. Regardless, each mode works the same way.
Some cameras have even more exposure modes with names like Full Auto, Portrait, Landscape, Macro, Action, or even (yes it’s true) Food. These are all fully automated exposure modes aimed at photographers who don’t know how to use the four inside the white area. The idea is that you can just match the exposure mode to the subject you’re shooting and the camera decides what ISO, aperture, and shutter speed to set.
These modes are best avoided if you want more creative control over your photos.
For example, in the portrait below I wanted to set the aperture to f/2.8 to blur the background. Aperture Priority is a good option, and if your camera has Auto ISO you could also set the shutter speed to say 1/180th of a second and let the camera work out the ISO.
Automatic, semi-automatic and manual exposure
Programmed Auto is a fully automatic exposure mode. The camera decides which ISO, shutter speed, and aperture to set. The difference between Programmed Auto and any of your camera’s fully automatic exposure modes (Full Auto, Portrait, Landscape, etc.) is that Programmed Auto lets you override the selected settings if you need to. The camera makes the decisions but gives you control over the result.
Aperture Priority and Shutter Priority are semi-automatic exposure modes. You choose and set at least one variable (aperture or shutter speed and perhaps ISO) and the camera sets the others.
In traditional Manual mode, you set the ISO, aperture, and shutter speed. The camera tells you via a viewfinder display whether it thinks your exposure settings are correct, but the final decision is down to you, the photographer.
When is Manual Mode not fully manual?
Around 10 years ago camera makers started adding Auto ISO to their cameras. So now you can set the aperture and shutter speed yourself, and let the camera choose the ISO. Even though it’s still called Manual, you’re not truly in a manual exposure mode anymore. It’s now a semi-automatic exposure mode that asks the camera to decide which ISO to use.
It’s a bit of an anomaly, but I guess it’s easier to leave Manual Mode where it is on the Mode dial than add another, new, exposure mode called something awkward like Dual Aperture and Shutter Priority.
You can see an example of where Auto ISO comes in handy with the portrait above.
Hopefully, this article clears up any confusion you might have about the difference between metering modes and exposure modes on your camera.
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