The aperture of a camera is the opening in the lens that lets the light through to the digital sensor (or film). The larger the hole, or aperture, the more light gets through to the sensor.
Aperture in lenses is measured in what are known as f stops. All lenses have various f stop ranges printed on the front. These numbers (e.g. f3.8-f5.4) tell you the range of the aperture of that lens.
There is a slight confusion in that the smaller the f number , the bigger the hole is in the camera and the more light it lets through. Therefore high f stops (e.g. f22) are small holes and let little light through.
Why do we care about aperture?
Well, aperture affects several things in our pictures:
1. Shutter Speed
The larger the aperture (e.g. a low number such as 2.8) the bigger the hole in the lens allowing lots of light onto the sensor. This increase in light allows us to have a quicker shutter speed in order to get the right exposure.
A quicker shutter speed will allow us to take better shots in low light conditions as any blur from camera shake will be minimized. This is particularly useful if taking pictures of people or moving things indoors or at night.
As a rule of thumb you should aim to have a shutter speed of no slower than 1/60th of a second if you intend to shoot hand held. Any slower and you may end up with a blurred image.
2. Depth of Field
Larger apertures reduce the depth of field of our pictures. If you are taking portraits or close ups of objects this is very useful as it allows us to blur out distracting backgrounds. This helps emphasize the subject of our pictures and train the views eyes towards our subject. So to blur a background you should try and select a high aperture (low f number) such as f2.8.
Large Aperture = Small f Number = Shallow Depth of Field
When shooting portraits large apertures help to blur distracting backgrounds. When doing so it is crucial to focus on the subjects eyes. The above photo was shot at f1.8. You can see that the depth of field is so shallow that while the subjects open eye is in focus, his closed eye is out of focus, despite being only a few milimeters in front.
How can we use Aperture?
Adjusting the aperture is one of the most powerful settings on your camera. The best way to explore and play with this feature is to use the Aperture Priority setting on your digital SLR.
First you need to set your mode dial to AV (AP on some cameras). Once that is done you should be able to adjust the aperture by using the dial on the right hand side of the LCD screen. As you move the dial you should see the f-number on the LCD screen (or in the view finder).
Once you have set the aperture, the camera will automatically adjust the shutter speed in order to get the right exposure. Usually it will do a pretty good job however depending on the conditions you may want to make further changes to other settings to improve your results.
If you half press the shutter button your camera should display the required shutter speed for the current light conditions. As mentioned above if the speed is below 1/60th of a second you should consider using a tripod or selecting a larger aperture (lower f number) to avoid getting a blurred shot.
Changing the ISO
If you are shooting in a low light environment such as indoors you may find that you have selected the maximum aperture and still cannot get a quick enough shutter speed to avoid a blurred shot. Do not fear because you can always up the ISO.
Increasing the ISO setting makes the sensor of your camera more sensitive meaning more light gets processed. The one downside is that at higher ISOs (800-1600) you tend to get more noise in your images which can lead to a grainy appearance. Therefore try to use ISO as a last resort and where enough light is available always shoot at ISO 100.
Summary
Aperture priority mode is incredibly powerful, letting you utilize the your cameras built in light meter while also giving you the creativity to control things such as the depth of field.
When using this mode however the camera can sometimes get it wrong. In order to gain even more control over the exposure we recommend that you familiarize yourself with your cameras exposure compensation mode.
If want to take more control over your digital slr then we would highly recommend reading what are considered seminal works in the photgrapy world: Understanding Exposure by Bryan Peterson and The Moment It Clicks by Joe McNally. Also don’t forget to take a look at our guide to using your cameras manual mode.
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