When you are first starting out with a DSLR camera, the number of settings available can be a bit daunting. However, most of these are only affecting one thing: the exposure. Understanding how exposure affects your images, and how to control it, is the first step to mastering photography and will underpin your photos for years to come. So what is exposure, and how can you manipulate it to get the image you want?

What is Exposure

So, before we delve into the nitty-gritty of controlling your DSLR, it is important to understand what exposure is. Fundamentally, exposure is how light or dark your photograph is, or in other words, how much light is used to take the picture. Your camera uses three settings to control the exposure: the aperture, the shutter speed, and the ISO. Together they form what photographers call the exposure triangle, and it is the combination of each of these that largely dictates the look of the final image.


The first in the exposure triangle is the aperture, the name given to the small hole where the light enters the camera body. Unsurprisingly, to create a darker image the aperture needs to be smaller and to create a brighter image it needs to be bigger. However, this is not the end of the story! The aperture size also affects the proportion of the photograph that is in sharp focus, known as the depth of field. A smaller aperture increases the depth of field (more of the image is in focus), and vice versa.

The aperture size is measured in something called f-numbers and can be a little confusing until you get used to it, as a bigger number indicates a smaller aperture. For many of us it’s just a case of remembering this quirk, but for the mathematically minded, you can understand it as the ratio of the fully open aperture. So, for example, an aperture with an f-number of 2 (often written as f/2) is half the full diameter, an aperture of 4 would be a quarter and so on.

Shutter Speed

The shutter is the small part of the camera that opens up to allow light in to take the photo. The shutter speed is simply the length of time the shutter remains open, so, the longer the shutter speed, the more light is allowed in, and the brighter the result. However, increasing the shutter speed also results in motion blur in a photograph, as objects may move while the shutter is open.


The final piece of the exposure puzzle is the ISO, a piece of technological wizardry that manipulates how sensitive the software is to the incoming light. However, like the other two aspects of the triangle, there is a payoff. While a high ISO will allow more light in, it also degrades the quality of the photograph, resulting in a noisy, or grainy, image. With improving technology, this level of degradation becomes less noticeable, so its classification as high ISO changes from camera to camera. However, the principle remains the same: the lower the ISO, the clearer the image.

Putting it together

How this all ties together largely depends on the type of photograph you are looking to take. A landscape photo may require a small aperture setting to increase the depth of field so that everything remains in focus. However, this may mean you need a longer shutter speed to allow in enough light. Conversely, if you are taking a wildlife shot, you will need as fast a shutter speed as possible to avoid any motion blur as the animal moves, which will require a large aperture. However, this reduces the depth of field, so if this is not the effect you are after, you will need to increase the ISO. Getting confused yet? It can be complicated to get just the effect you are after.

There is one general rule though, and that is to keep the ISO as low as acceptable. If you can get the effect you need just by tweaking the aperture and shutter speed, then that is what you should do to maintain image quality. However, remember that the ISO is also a valuable tool, and for some shots, you may not even be able to notice the bit of noise that it introduces.

At the end of the day, like any aspect of photography, it is all about getting out there and practicing. A good exercise is to take lots of photos of the same thing with different settings so you can get a feel for exactly what is happening when you make any changes. Transfer the images to your computer as well so you can have a good look at the level of detail of each combination of settings. Fortunately, it doesn’t take too much practice to grasp the basics of the exposure triangle, and when you do, the fun of photography truly starts.


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