Controlling exposure: metering modes
In the second part of our series on controlling exposure we’re looking at how exposure metering works and metering modes. Understanding your camera’s exposure meter is essential to understanding how your camera works and then moving on to photographing in manual mode.
But let’s not jump in at the deep end yet. Let’s first understand how exposure metering works and why you need to know it.
If you missed part 1, you can find it here – Understanding the exposure indicator
What is meant by exposure metering?
When you measure the exposure of a scene, you are measuring the brightness of a scene so that either you (in manual mode) or your camera (in all other modes) can set the aperture, shutter speed and ISO for a correct exposure. If the scene is not measured accurately your photo will be underexposed or overexposed.
There are two ways of measuring brightness of a scene:
- a handheld light meter
- your camera’s inbuilt metering system
In this article we’re specifically looking at how a camera meters light, which is the light reflected off the subject, in different metering modes.
In auto you have no control over exposure metering, which is why it’s best not to use auto. You can set metering modes for your camera’s metering system in:
- program mode
- aperture priority mode
- shutter priority mode
- and of course manual mode
What does metering mode mean?
A metering mode is the camera setting you choose to measure exposure. When you select a metering mode to measure the brightness of a scene, you decide what part of the scene you want correctly exposed. So deciding on a metering mode is your first decision when setting exposure.
What are the different metering modes?
There are three exposure metering modes for Nikon and four for Canon. The symbols for the different metering modes vary between brands, as do the names:
- Spot metering
- Partial metering (Canon only)
- Center-weighted metering
- Matrix metering (Nikon), evaluative metering (Canon), zone metering (Sony)
What’s the difference between the metering modes?
Meters the brightness of a specific area that you’ve selected, which is about 2 – 4% of the scene.
Use this when the light is coming from behind your subject, like when you’re indoors photographing a subject in front of a window. Your background may be overexposed, but your subject will be correctly exposed.
Further reading: When to use spot metering?
Partial metering (Canon only)
Meters 8 – 13% of the center of the scene.
This, like spot metering, is really useful when your subject is darker than the background, such as when your subject is backlit.
Meters the area around the center of the scene, which is about 60 – 80% of the scene, regardless of your focus point.
Matrix metering (Nikon) or evaluative metering (Canon)
Meters the overall brightness of the entire scene, so is ideal when the scene is lit from the front.
Learning when to use each of these types of metering will make a big difference to your photography.
What’s the point of different metering modes?
If the camera knows what part of the scene you want correctly exposed, it will be more able to do what you want it to do. Having a choice of different metering modes to use in different situations gives you the ability to meter the exposure in part or all of the image, depending on your needs.
Things to watch out for
Because your camera measures reflected light and is designed to average the exposure out to an average midtone (that’s medium gray if you’re thinking in black and white), it will struggle when the scene is either dark or light.
Easy to meter scenarios are scenes without much contrast between light areas and dark areas, such as a brick wall, your back garden on an overcast day, a green landscape. Anything that is evenly lit and doesn’t have huge variations between lights and darks.
Because your camera measures the scene to expose it at an average tone, when faced with a dark scene, it might overexpose the scene as it tries to lighten the dark tones.
On the other hand, if the scene is very light, such as a field of snow or a white building, your camera will read this as very bright and will underexpose the scene.
Knowing this allows you to take control when faced with challenging situations for your camera’s exposure meter.
You have three choices to help your camera measure a scene correctly:
- Meter off a midtone within the scene
- Meter off a gray card
- Use exposure compensation
We’ll look at the first two below, but will look at exposure compensation in part 3 of this series on controlling exposure.
Where to find midtones in a scene
- Healthy green grass
- Gray wall
- Skin (as long as it’s not too fair).
How to meter off a midtone in a scene:
- Select spot metering on your camera
- Point it at the midtone area to assess the exposure
- Adjust your ISO, aperture and shutter speed as needed
- Start shooting
What is a gray card and how to use it for exposure metering?
Gray cards are exactly that – medium gray non reflective material.
They don’t cost much and can be bought from from a camera dealer, or online. I use a Lastolite fold away gray card that looks like a really small pop up gray reflector (it’s the Lastolite EzyBalance 12 inch – 18% Grey / White).
How to use a gray card if you’re photographing a person:
- ask them to hold up the gray card
- aim your camera at the grey card
- put your camera into manual mode
- meter the exposure
- adjust ISO, aperture and shutter speed
- focus and start shooting
If the light changes, or you change your position, meter again, but otherwise you’re good to go.
How to use a gray card if you’re photographing a scene without a person in it:
- position the gray card in the scene facing you
- meter off it as above
- remove it from the scene and start shooting
Further reading: How to use a gray card to meter exposure
Don’t miss out
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Missed Part 1? Here it is…
Read Part 1 of Controlling Exposure – Understanding the exposure indicator
Part 3 – How and when to use exposure compensation
The exposure metering system on your DSLR camera can be fooled, such as when shooting in snow.
We look at the different situations that will confuse your camera and what you can do about it. This is exposure compensation.
Part 4 – How to control exposure in all shooting modes
Maybe you want a faster shutter speed or shallower depth of field?
The camera doesn’t know how to achieve creative results, it only knows how to give an accurate average exposure reading for the area that’s being metered.
We look at when and how to use program mode, aperture priority, shutter priority and manual mode for creative results and controlled exposure.
Part 5 – Pros, cons and how to use auto ISO
Sometimes there’s so much going on that you need a little auto help. We look at the benefits and limitations of using auto ISO – even in manual mode!
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