Metering modes and how exposure metering works (control exposure)

Controlling exposure part 2: metering modes

In the second part of our series on controlling exposure in photography 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 before 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 for exposure camera settings and why you need to know it.

For maximum benefit from this article, you first need to know how to read your camera’s exposure meter.

What is meant by exposure metering?

Metering exposure for photography is measuring the brightness of a scene. Once you know how bright it is you can adjust your camera’s exposure for a correct exposure.

In manual mode you make the adjustments to aperture, shutter speed and ISO. However, in all other modes your camera takes the responsibility for correct exposure settings, some more so than others.

If you don’t measure the exposure accurately your photo will be underexposed or overexposed.

You can measure the brightness of a scene with:

• A handheld light meter (meters incident light)
• Your camera’s inbuilt metering system (meters reflected light)

In this article we’re specifically looking at how a digital camera meters light, which is the light reflected off the subject, in different metering modes.

You can set metering modes for your camera’s metering system in:

• Program mode
• Aperture priority mode
• Shutter priority mode
• Manual mode

In auto mode you have no control over exposure metering, which is why it’s best not to use auto 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?

Nikon has three exposure metering modes and Canon has four. The symbols for the different metering modes vary between brands, as do the names.

The different camera metering modes are:

1. Spot metering
2. Partial metering (Canon only)
3. Center-weighted metering
4. Matrix metering (Nikon), evaluative metering (Canon), multi-zone metering (Sony)

What’s the difference between the metering modes?

Spot metering

Spot metering mode meters the brightness of a specific area that you’ve selected, which is about 2 – 4% of the scene.

In portrait photography the subject is the most important part of the image, so must be correctly exposed. Spot metering is therefore the most used metering mode for portraits.

To use spot metering for a person place the metering point on your subject’s cheek, just below the eye.

Spot metering is particularly helpful when light is coming from behind your subject. For example, when indoors photographing a subject in front of a window. Metering for the subject will make your background overexposed, but your subject will be correctly exposed.

Partial metering (Canon only)

Partial metering measures 8 – 13% of the center of the scene.

Partial metering, like spot metering, is really useful when your subject is darker than the background, such as when your subject is backlit.

Center-weighted metering

Center-weighted metering measures the area around the center of the scene, which is about 60 – 80% of the scene, regardless of where your focus point is.

Matrix metering (Nikon), evaluative metering (Canon), multi-zone metering (Sony)

Matrix metering mode (aka evaluative metering or multi-zone metering) measures the overall brightness of the entire scene, so is the ideal metering mode to use when a scene is lit from the front.

Learning when to use different metering modes will make a big difference to your photography.

What’s the point of different metering modes?

Setting the correct metering mode tells your camera what part of the scene you want correctly exposed, so it’ll be able to do what you want it to do.

Having a choice of different metering modes for 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’ll struggle when a scene is:

• High contrast
• Dark
• Bright

High tonal contrast scenes

Easy to meter scenarios are scenes have low to medium dynamic range, without much contrast between light areas and dark areas. In other words, anything that’s evenly lit and doesn’t have huge tonal contrast between lights and darks, such as:

• A front lit brick wall
• Your back yard on an overcast day
• A green landscape

Dark scenes

Your camera measures a scene to expose it at an average tone of medium gray. So when faced with a dark scene, it wants to overexpose the scene to lighten dark tones to medium gray.

Light scenes

When a scene is very light, such as a field of snow or a white building, your camera reads this as too bright and wants to underexpose the scene to make it medium gray.

Knowing how your camera wants to expose a scene allows you to take control when faced with challenging lighting situations for your camera’s exposure meter. Understanding how to use the zone sysmem will help you to see the world as your camera does so you can make more informed exposure decisions.

3 ways 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 how to use exposure compensation in part 3 of this series on controlling exposure.

Where to find midtones in a scene

When you convert images to black and white it’s easy to see midtones, because they’re the middle gray areas of the image. However, when you’re looking at a color scene, it’s difficult to know, unless you know that midtones in a natural light image outdoors will be:

• Healthy green grass
• Light stone wall
• Blue sky (with the sun behind you)

How to meter off a midtone in a scene

Once you’ve spotted a midtone area you simply need to measure the reflected light from the area with your camera’s exposure meter to set your exposure. Here’s how:

• Select spot metering on your camera
• Point it at the midtone area to assess the exposure
• Adjust your ISO, aperture and/or shutter speed as needed
• Start photographing

What is a gray card and how to use it for exposure metering?

Gray cards are exactly that – medium gray non-reflective material that you hold in front of the camera to measure exposure. If there’s no midtone in the scene to meter for a correct exposure, it’s really helpful to have a gray card on hand.

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% Gray / White).

How to use a gray card for portrait photography:

• Set your shooting mode (manual, aperture priority, shutter priority or program mode)
• Ask your subject to hold up the gray card
• Aim your camera at the gray card and zoom in to fill the frame
• Meter the exposure
• Adjust exposure settings (ISO, aperture and shutter speed) depending on your shooting mode
• In aperture priority, shutter priority and program modes you’ll need to lock exposure
• Focus and start photographing

If the light changes, or you change your position, meter again, but otherwise you’re good to go.

Before taking a photo, get into the habit of asking yourself what metering mode would be best for the situation.

How to use a gray card without a person in the scene:

• Position the gray card in the scene facing you
• Meter off it as above
• Remove it from the scene and start photographing

Don’t miss out

If you don’t want to miss when new photography tutorials are published, pop me your email address. You’ll receive our metering mode cheat sheet instantly as a bonus and every week I’ll send you my bulletin of helpful tutorials to keep you on track to taking the photos you dream of.

 

How and when to use exposure compensation

The next step in controlling exposure is understanding how the exposure metering system on your DSLR camera can be fooled, such as when shooting in snow.

In the next article we look at the different situations that’ll confuse your camera and what you can do control it with exposure compensation.

How to control exposure in all shooting modes

Once you know how to control exposure, you can get creative with the exposure settings for particular looks or scenarios. Maybe you want a faster shutter speed or shallower depth of field?

Digital cameras don’t know how to achieve creative results, they only know how to give an average exposure reading for the area that’s metered.

Here’s how to use program mode, aperture priority, shutter priority and manual mode for creative results and controlled exposure in all shooting modes.

Pros, cons and how to use auto ISO

Sometimes there’s so much going on that you need a little auto help from your camera. So it helps to know the benefits and limitations of using auto ISO – even in manual mode!

Leave a comment

If you have any questions about the best metering mode to use or how to use the different metering modes for portrait photography, leave a comment and I’ll get back to you with some help.

Also, I love good news, so if my exposure metering tips have helped you to understand how exposure metering works, share that too.