Understanding exposure compensation

Modern digital cameras do a great job at getting the exposure right — most of the time. Here’s how to get great shots the rest of time.

Why your camera sometimes gets it wrong

Imagine that everything you saw around you was made of paint. Scoop up all that paint and stir it up, and the resulting gooey mix would most likely turn out to be a boring mid-toned grey.

That’s how your camera thinks. It samples the amount of light and dark it ‘sees’ in a scene and assumes that when everything gets mixed and averaged out the result should be not too dark, not too light. Just a neutral grey. If it averages out lighter than that, then it decides there’s too much light coming through the lens and so it reduces the exposure. And if things average out into a dark tone then it increases the exposure.

Because most scenes contain a balanced mix of light and dark objects, this averaging-out method works pretty well and that’s why the exposure will be pretty much right, more often than not. But what if you’re photographing a scene that only has light-toned things in it? Like for example, a white rabbit on snow.

The camera will ‘see’ white, white and more white and when it averages that all out, it ends up with, you guessed it: white! It decides that just can’t be right because it’s been programmed to think everything should always average out into mid-toned grey. So it reduces the exposure. The result will be a photo that is badly underexposed, with a grey rabbit against grey snow. So now the camera’s happy, but you’re not.

How to fix it

The good news is that your digital SLR (and some of the smarter compacts) will most likely have a function called Exposure Compensation.

At this point you’ll need to look at your camera’s manual to find out how to activate it. Once you know how to turn on that setting in your particular camera, here’s what you do with it.

First of all, you’ll see that exposure compensation is measured in ‘stops’. Stops is a word that refers to your aperture settings.

If your camera keeps making things too dark, you increase your exposure by setting your camera’s Exposure Compensation to a positive number of stops.

And if you want to decrease your exposure you set it to a negative value.

Usually, one stop will make a world of difference to your photo and you can test if you need more or less by taking a shot and glancing at your histogram. If you need help on histograms, a guide to understanding them can be found here.

With a bit of practice in photography, you’ll soon start noticing the kinds of situations where your camera is likely to get things wrong, when Exposure Compensation is needed. The examples below illustrate some of the situations to look out for.

Extremely bright background

When I saw the Little Pied Cormorant shown above I knew the camera would have trouble with it. Not only was the bird back-lit, meaning that the part of the bird I could see was in shadow, but sunlight was reflecting off that water behind it, throwing up a huge amount of glare. I knew that bright glare was going to cause a problem with the camera’s automatic exposure settings. Leaving the camera with its default settings would have given me the underexposed photo shown at left.

In a perfect world, I’d have used a flash to light up the front of the bird, but the bird was a long way away and I knew the little pop-up flash on the camera wouldn’t reach it.

So I set Exposure Compensation to +2 stops. The result was the pic at right, where the water is now pushed almost to white, and the bird is correctly exposed.

What to look out for:

A glaring bright sky background or glare reflected behind your subject, is a sure sign you need to either use a fill flash or turn to Exposure Compensation

The theory:

All that glare should be near white, but the camera would have wanted to turn it into a much darker mid-tone. So I needed to brighten things back up again. That’s why I used a positive Exposure Compensation setting.

Bringing out the detail in a white texture

When an area of white texture is hit by bright sunlight, the camera will often ‘blow out’ the detail. Once an area of white is overexposed that much you’re unlikely to ever get any detail out of it. Even pushing the area through your image editing program won’t help.

So in this case, I deliberately underexposed the shot a little in order to show the detail in the feathers. So I set Exposure Compensation to a minus amount (- 1/3 stops)

What to look out for:

An area of textured white area within a scene dominated by darker tones

The theory:

I didn’t want blown-out white areas in my photo and so, when confronted with a bird that had so many white feathers, I deliberately underexposed the shot slightly.

How do you know if you should make things darker or lighter?

If the scene contains nothing but white objects on white backgrounds (white rabbit in the snow), make it lighter (to counteract the camera’s tendency to underexpose this kind of shot). That means a positive number of stops in Exposure Compensation.

If the scene contains nothing but dark objects on a dark background (black bug on a black wall) then make it darker (to counteract the camera’s tendency to overexpose this kind of shot). That means a negative number of stops in Exposure Compensation.

To highlight detail in a dark texture: Make it lighter (positive number of stops in Exposure Compensation)

To highlight detail in a light texture: Make it darker (negative number)

Too confusing? Can’t remember all this? Then choose a setting of about a stop up or down, and fire off a test shot. You’ll quickly see by looking at the preview on your camera’s screen (and the histogram) if you were on the right track

Beginners’ series on
digital SLR photography

• A beginners’ guide — basics for Digital SLRs
• Learning from examples — picking up where the first article left off
• Understanding histograms — making sense of this handy tool
• Preventing washed-out photos —Why it happens, and how to prevent it
• Understanding Exposure Compensation — Why your photo subject can look so badly exposed, and what to do about it
• Megapixels — how many is enough?

Photo Sales

• Photo Library — Pics of Australian critters

An unhelpful guide

• Wildlife Photography — this guide will not make you into a better photographer
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