Exposure is how much light is allowed to hit the camera sensor when recording an image. The photograph’s exposure will determine how dark or light an image will appear when it’s been captured by a camera sensor. Three settings allow you to control the camera exposure of your photo – aperture, ISO and shutter speed. By adjusting the aperture, ISO and shutter speed you can change the exposure of your photo, meaning you can control how light or dark your picture will be. These three camera settings make up what is known as the exposure triangle.
The exposure triangle
Trying to find the correct camera exposure can be like a juggling act. As you decide aperture, you will also need to adjust shutter speed and then ISO. Achieving the camera exposure you want for a photograph is all about balancing the exposure triangle.
With all the automatic settings modern cameras come with, why would we want to control the exposure of our photos? Why go to all the trouble of finding a great photograph to take and then allow your camera to decide how it should look.
Image of the exposure triangle from www.cliftoncameras.co.uk
By learning to balance the exposure triangle, you will have greater control over the look and feel of your photographs. Exposure is not the only role that aperture, ISO and shutter speed play in photography.
ISO is how sensitive the camera sensor is to light. Increasing ISO allows for faster shutter speeds in lower light levels. As you increase ISO, though, you also increase the digital noise visible in the photograph.
Aperture controls the diaphragm of the lens; this controls the amount of light that is allowed to travel through the lens. As you increase aperture, you let less light into the lens. You will also change the depth of field of the photograph.
Shutter speed is the speed at which the shutter closes. The longer you keep the shutter open for, the more light is let in. The longer the shutter is left open for, the more camera shake will blur your photo.
By understanding how these elements affect camera exposure and the look and feel of your photos the more control you can have on your photography. You can learn more about each part of the exposure triangle in our in-depth guides but here is a brief overview of each setting.
ISO stands for International Standards Organisation. That is the body which standardises sensitivity ratings for camera sensors. On a camera, ISO is the rating given to light sensitivity and ranges from 25 to 3200 (and above). The lower the rating means, the less sensitive the image sensor is and this creates a smoother image because there is less digital noise. When the ISO rating is higher, the more sensitive the image sensor is, and this produces more digital noise. Digital noise becomes more noticeable in low light conditions compared to stronger light sources.
Digital noise is any light signal that does not come from the subject area of the picture. Just like film, digital camera sensors are designed to perform best at the lowest ISO rating. For most digital cameras this is ISO 100, but some high-end DSLR’s have ISO’s that go as low as 25.
Low ISO works well in daylight photos; you can easily operate with an ISO in the 100 – 400 range. In lower light, it can be harder to keep your ISO in a lower range. By using the other settings on your camera, you can allow more light into the camera sensor and still use a low ISO rating.
To reduce the digital noise in a photograph, lower the ISO. Ideally, you’d like to stick with an ISO between 100 to 400, but you will have to adjust other settings in low light conditions. There is no correct camera exposure or no perfect group of settings. Experiment with the settings and find an exposure or style that you enjoy in your photos and use that.
The aperture of a lens is the opening in the diaphragm that sets the amount of light that passes through the lens. Aperture is measured in f-stops and the smaller the f-stop (f/4 for example) the larger the opening so, the more light that passes through the lens. The higher the f-stop (f/22 for example), the smaller the opening and of course that means less light goes through the lens.
While aperture is controlled on the digital camera the maximum, and the minimum aperture is determined by the lens. Bear this in mind when shopping for a lens.
Aperture helps a photographer control the lighting and the feel of a photo. A smaller aperture is good for portraits as it will bring the subject into sharper focus while blurring the background. For landscapes, you will want the whole scene in sharp focus so you will use a higher aperture.
The shutter sits just in front of the imaging sensor, and it determines the length of time the sensor is exposed to light. Shutter speed is measured in fractions of a second. It has a vast range; some DSLRs can shoot at 1/8000 which is incredibly fast and as slow as 30 seconds. When the shutter speed is faster, the image will be sharper, and when it is slower, the image will be blurry.
Shutter speed will give you incredible options of creative control. Fast shutter speeds can create fantastic action shoots by ‘freezing’ motion in your image. By using a tripod, a slow shutter speed can be used to create beautiful images such as light trails.
As with the other two settings, shutter speed allows a photographer to control exposure. It also gives creative options for every picture you take. Sharper images may not always be best, and blurring is not always a bad thing. The choice is always up to the photographer.
Modern DSLR cameras come with an extra option to help you achieve your optimal exposure. Exposure compensation allows you to adjust your exposure by smaller increments. This can help make final adjustments to further enhance your use of the camera settings.
The histogram on your digital camera is a representation of the pixels exposed in your photo. On the left side, blacks and shadows are represented, and the right side represents bright areas and highlights. The mid-tones are measured in the middle section. The height of the peaks on each section shows the number of pixels in that particular tone.
Most DLSR’s will allow you to see the histogram as you take your photo. This is an excellent guide to helping you find your preferred exposure for any given shot.
What is over or underexposed?
Here is the tricky part because the best exposure or the correct exposure is subjective. Despite this, some images are clearly over or underexposed. The highlights in a photo are unreadable when overexposed. Underexposed will work in the same way, there is no information stored in the shadows.
Those are the extremes of exposure. Correct exposure is the preference of the photographer but be aware that underexposure can hide detail in a picture and overexposure can cause a “watery” effect on a photo and diminish the colour.
If this all seems daunting (and for beginners it certainly can be) don’t worry because DLSR’s have semi-automatic modes that will do most of the work for you. By using ‘Shutter Priority’ mode, you will select the shutter speed, and the camera will select the best aperture setting. It works the same way with ‘Aperture Priority’, you control the aperture. In ‘Program’ mode, you can simply shift the combination of aperture and shutter speed with a spin of the camera’s control dial.
Modern cameras will also have an ‘Auto ISO’ mode so that you can focus on just one area of the exposure triangle at a time. This is a handy learning tool and will help you get used to thinking about the different settings for exposure, but the aim for any photographer should be to eventually move onto to manual mode and take full control of exposure.
Camera exposure key points
- As you change one setting, it will affect the others. If you use a fast shutter speed, you’ll need a larger aperture setting to allow more light to reach the sensor.
- For the aperture remember that a small f-stop is a large aperture setting and a large f-stop is a small aperture setting. Yes, it’s confusing at first, but you will soon get used to it.
- A fast shutter speed will freeze the action, and a slow shutter speed can create a blurring effect.
- The create a blurred background (bokeh effect) chose a small f-stop (remember that’s a large aperture).
- When shooting at very low shutter speeds, a tripod will be invaluable.
- Automatic modes can help you learn about how an individual setting can affect exposure and the feel of a photograph.