When and how to use spot metering for accurate exposure

It would be easy to say always use spot metering most of the time in portrait photography, but that’s not particularly helpful for learning why and when to use spot metering in photography. You need to know:

• Why spot metering is a good choice
• When it’s the only suitable metering mode to use
• How skin color affects spot metering
• The two times spot metering is not ideal

But first you need to know what it is.

What is spot metering in photography?

Spot metering covers the smallest area of all the metering modes as you measure just 2 – 4% of the frame.

Because the other metering modes measure much wider areas, they aren’t as targeted as spot metering.

The 3 main metering modes on your camera used for measuring the brightness of a scene and setting exposure are:

• Spot metering
• Center weighted metering
• Evaluative metering (Canon) or Matrix metering (Nikon) or Zone metering (Sony)

Canon is the only brand that also offers partial metering.

Unlike the other metering modes, the icon for spot metering is the same across all camera brands.

Further reading: Metering modes and how exposure metering works

Does spot metering work in manual mode?

All the metering modes work across the different shooting modes. They just work differently. So, yes spot metering works in manual mode.

In the semi-automatic and automatic shooting modes, once the camera has measured the scene based on the metering mode you selected, it adjusts the exposure settings. These are:

• Aperture mode
• Shutter priority mode
• Program mode
• Auto mode

In manual mode, you can see if your your exposure settings are accurate by looking at the exposure indicator. But it’s up to you to change either the aperture, the shutter speed or the ISO according to the exposure indicator’s recommendation for the correct exposure.

However, sometimes the exposure setting is wrong, because your camera can get confused in center weighted and evaluative / matrix / zone metering modes.

Which leads me to my next point…

 

Why use spot metering?

If the scene has both bright and dark areas, your camera will struggle to meter the scene accurately in the other metering modes.

It’s up to you as the photographer to decide if you want the bright areas or the dark areas to be exposed correctly.

• If you want an average exposure for the entire scene, use the default metering mode, which is evaluative / matrix / zone.
• If you want the central part of the image to be correctly exposed, select center weighted metering.
• To ensure that a very specific part of the image is correctly exposed, use spot metering, because it allows you to select and meter a small area.

Examples of when to use spot metering mode:

1. Spot meter when your subject is backlit

To avoid including the bright light behind your subject, which will influence the exposure reading, use spot metering to meter only your subject so that they’re not underexposed.

Bear in mind though, that without adding in fill light or reflecting light back into your subject, the background will be overexposed as it’s brighter than your subject.

Further reading: 

Using fill light – essentials you need to know

How to use a reflector properly and why you really need one

2. Spot meter when the background is very dark

On the other hand, if the background is dark and is included in the exposure measurement, the camera will want to brighten the background, which will overexpose your subject.

So, to avoid including the background in the exposure reading, use spot metering for an accurately exposed subject.

3. Spot meter when your subject is wearing very light or very dark clothing

Again, because the color of your subject’s clothing will influence your camera’s ability to meter the scene accurately, you’ll need to use spot metering to measure the exposure of your subject’s face only.

4. Spot meter when photographing in snow or at the beach

Because your camera wants everything to be average gray, it’ll want to underexpose the bright white beach sand or snow to medium gray if you allow it to measure the exposure with these areas included.

So with any metering mode, other than spot metering, in these conditions your exposure will be wrong.

To summarize, spot meter for portraits:

• When the subject is backlit
• In high contrast scenes

Is spot metering best for portraits?

In portraiture your subject is the most important part of the image, so must be correctly exposed, especially their face. Because such a small part of the scene is the most important part to be correctly exposed, spot metering is ideally suited to portrait photography.

As a portrait photographer I use spot metering at least 90% of the time.

However, sometimes the other metering modes are better.

2 times spot metering isn’t ideal for portraits

It makes sense that if spot metering worked for every type of photography in every scenario, they wouldn’t have developed the other metering modes. In portrait photography, there are 2 times when the other metering modes are a better choice. They are:

1. Documentary style photoshoots

Because spot metering involves such a small area, in a fast paced documentary style photoshoot, using spot metering in one of the semi-automatic modes could be difficult.

You’d have to pay close attention to what’s being metered as you move from one scenario to the next, which could slow you down or result in overexposed or underexposed photos.

If shooting in manual mode, once you’re really comfortable with moving spot metering and moving the point around, however, I’d still recommend spot metering.

2. Extreme close ups

If the portrait is an extreme close up of your subject, where their face fills the frame, spot metering is not essential and you can use matrix metering instead for an accurate exposure.

In fact, unless you shoot in manual mode, if your focal point also acts as the area to meter for spot metering, as with Nikon cameras, it would actually be better to use matrix metering.

In an extreme close up, you’d have to meter your subject’s skin, set your exposure, then focus and take the shot.

This is because in portrait photography we focus on the eye, but we meter for the skin. If you meter the eye, which is darker, your exposure won’t be correct, especially if your subject has light skin.

How skin color affects metering mode choice

Cameras see in black and white and their exposure system wants to make everything a medium gray. So your camera doesn’t like to record white as white or black as black. It’ll always try to bring both white and black back to gray.

What that means in portrait photography is that your camera will want to brighten dark skin to medium gray and darken light skin to medium gray.

Asian skin, in black and white terms, is medium gray, so your camera will expose this correctly.

Obviously there are many, many different skin tones, so this is a simplification, but it’s a good starting point for accurate exposure.

Knowing this, you can now take steps to help your camera expose correctly using exposure compensation. It’s a setting on your camera that allows you to adjust exposure up or down:

• Black skin: -1 exposure compensation
• Light Asian or tanned white skin: no need for exposure compensation
• White skin: +1 exposure compensation

Further reading for how exposure compensation works and the zone system to understand why:

How and when to use exposure compensation – controlling exposure part 3

How to use the zone system in photography for perfect exposure

How do you use spot metering?

How to set the metering mode varies between camera brands and even between models of the same brand. With higher end cameras you can select the metering mode using buttons and dials on your camera, but with entry level cameras you need to use the menu system on your camera.

Either way though it’s easy to do.

Before you begin, check your manual to see if the area your camera meters is at the very center of the frame like Canon, or if, like Nikon spot metering, it moves with the focal point.

It’s a three step process once you’ve selected your metering mode:

1. Meter
2. Adjust camera settings
3. Take photo

1. Meter

• If the light on their face isn’t even, such as when it’s hitting only one side of the face, decide which side you want to expose for
• Position the spot on the cheek you want to expose for to take a meter reading
• Take note of skin coloring

2. Adjust camera settings

• Underexpose by 1 stop for black skin and overexpose by 1 stop for white skin. Asian skin won’t require any exposure compensation
• In manual mode, once you’ve taken the reading and adjusted your settings accordingly, you’re good to go. As long as the light stays the same on your subject you can continue to photograph without having to measure again
• In program, aperture priority or shutter priority adjust exposure compensation for skin type, then lock in the exposure using the Auto Exposure Lock (AEL or AE-L) button so that your settings don’t change as you reframe the shot. For this reason, manual mode is best when using spot metering, especially if you also use back button focusing 

3. Take photo

Although spot metering is ideal for when your subject is backlit, the process is the same no matter where the light is coming from.

Further reading: 

How to use AE lock (auto exposure lock) for easy exposure

Back button focus – how to use it and why it’s your BFF

Which metering mode is best?

Every metering mode has its place, but for portrait photography spot metering mode is best most of the time, especially if you photograph in manual mode.

That said, when it comes to shooting style, so many factors influence the camera setting decisions you make, including subject, lighting, activity and simply what makes you feel comfortable and confident.

So, what works for one photographer might not work for another.

Only practice and time will help you to decide for yourself …but meanwhile, get to know all the metering modes.

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