Understanding Exposure

By Chad Cocking

If I look back at more than a decade spent taking wildlife images, I believe that there are a handful of elements that, once I understood them, greatly shaped my photographic path. They are:

  • Good compositions
  • Not cutting the animals’ feet off
  • And, most technically, an understanding of the camera’s exposure

Although we will discuss the first two elements at a later stage, it is pertinent to begin this series with one of the more technical aspects of photography - exposure. Once you understand exposure and how the camera sees the world, you will then be in a better position to be in control of the images that you produce.

When we talk about exposure, we are essentially talking about how much light is received by the camera’s sensor. This is ultimately controlled by three factors; how long the camera’s shutter is open for (referred to as shutter speed), how much light is being let through the lens (the aperture of the lens), and the camera’s sensitivity to light (determined by the ISO setting). These three factors work in conjunction with one another to produce the final exposure of an image created by the camera.

An alteration of any one element needs to be compensated for by a concurrent change in one of the other two in order to maintain a constant exposure. This is best illustrated in the diagram below where the relationship between each of these elements can clearly be seen.

To help our understanding of exposure, we need to realise that the modern-day camera is essentially a computer that does not see the world quite as our brain-linked eyes do. In essence, they are similar in that both our eyes and the camera’s sensor record light, but we have an incredibly high-powered brain that is able to look at all the various elements within a scene and reconstruct the objects to produce the image that we ultimately perceive. This process is much more than simply recording the light in the cells of our eyes (as is the case with a camera’s sensor).

The fact that our eyes see the world differently to the camera means that sometimes when we look at our pictures we are disappointed with what the camera has captured because it barely matches the moment that our eyes (and brain) witnessed. I’m sure that there has been more than one occasion when you have shown someone a photo that you took of a gorgeous sunset and said “but the picture doesn’t do it justice”.

The truth is that the camera could have done the sunset justice if it had been given a helping hand. After all, the camera is just a computer and didn’t know it was looking at a stunning sunset.

For the most part, the camera’s computerised brain will get the scene and the exposure just right, and it does this by seeing the world not in colour, but rather in shades of grey.

To the camera, 18 percent grey has been deemed the average exposure and, as a result, it will try to expose all scenes to approximate an 18 percent grey tone unless told otherwise.

When it comes to an everyday front-lit scene, this average exposure will come out just as our eyes are perceiving it, and we have no issue with the camera’s ability. Such typical scenes might be that of a herd of impalas grazing in a green grassland, or a pride of lions in a dry winter landscape.

A mid-toned lioness in a mid-toned environment is a situation that the camera’s built in exposure metering will usually get correct

A front-lit waterbuck in a green landscape is one full of mid-tones that will not confuse the camera

There are, however, times when the scenes that we are photographing are not average, and the camera produces images that are either too light or too dark, and an incorrect exposure is attained. These results can be referred to as being over- and under-exposured respectively.

When an image is over-exposed, it appears too bright and is a result of the camera having recorded too much light. Over-exposure occurs most frequently when we have a dark-toned element (somewhat darker than 18 percent grey) that dominates the scene that we are attempting to photograph.

The camera does not know that this element is actually a darker-than-average tone and tries to compensate for this by representing the dark part of the scene as a mid-toned, 18 percent grey area. This dark object has now been depicted as being lighter than it actually is and everything else in the scene is lightened up too. We then end up with a horrible, washed-out image.

The darker-than-average background shadows confused the camera’s metering. In trying to brighten up the shadows, the entire image of this elephant calf became slightly over-exposed 

The prominence of the giraffe’s silhouette in this image led the camera to attempt to brighten the generally dark scene, and this ended up washing out the afternoon sky

The most frequent instances when over-exposure occurs are when we are photographing dark coloured animal scenes (such as buffalos and elephants) with lots of dark shadows in them (such as a side-lit scene), and sunsets with a silhouetted horizon.

Conversely, an under-exposed image occurs when the camera has not recorded enough light, and the end result is an image that is far darker than we wanted. This happens when objects that are lighter than 18 percent grey dominate the scene we are photographing – such as a white bird, a brightly back-lit scene, or most commonly, bright blue sky. In an effort to depict these light coloured elements as average, the camera darkens them to an 18 percent grey tone and, as expected, this darkening of the lighter elements results in an overall dark image.

Photographing birds against a blue sky is always difficult. The camera will attempt to darken the sky to a more average mid-tone, with the result being that the subjects come out very dark and under-exposed 

In trying to expose the dominating skyline as mid-toned, the dark foreground becomes way to dark in this under-exposed image

The good news is that even though the camera is bound to make mistakes with its exposure from time to time, there are a number of ways that we (as the operator of the camera) can help the situation by applying corrective measures to the exposure.

In the beginning, this is most easily done by checking the exposure of the images on the camera’s display screen to see if the image is over- or under-exposed, and then making changes to correct this before taking the next photo. As time goes by and you get more experienced, you will be able to pre-empt the camera’s response to a particular situation, and make the exposure adjustments before you even take the photo! 

To prevent this wet, young elephant calf from being over-exposed in the image, I adjusted my exposure compensation to -0,7 to ensure that the dark areas stayed dark

This bright, colourful sky and pitch black foreground silhouettes offers tricky exposure to get right, but knowing that the camera would try and expose the silhouettes much lighter than they actually were, I pre-emptively set the exposure to -1,7 to keep the blacks black, and prevent the sky from becoming too bright (over-exposed)

The exact methods we will use for making these exposure adjustments will be discussed a little later in this series but for now, it is sufficient to simply mention that the two most useful methods for getting the correct exposure are:

  1. Spot metering
  2. Exposure compensation

So if you are still with us, congratulations for having made it through what will be, without a doubt, the most technical of these blog posts. With this information in hand, your enjoyment of wildlife photography will be greatly enhanced. When things start going awry from an exposure perspective, you should now be in a position to understand them, and make the corrections needed to get the wildlife photographs that you want to take!

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