ePHOTOzine Photography Academy- Aperture explained

What is an aperture?
The aperture is the name used to describe the size of the diaphragm (the opening, or hole, which allows light through to the sensor). Apertures are measured in F-stops.  F-stops are measured in incremental, numerical steps but to make things a little more confusing, the higher you go, the smaller the hole which lets the light through. Which, even though it may seem a little odd, means by selecting a higher number less light will be let through onto the sensor.

For example:

In a nutshell, the larger the hole, the lower the number will be and vice-versa.

Why do I need to use apertures?

Move the slide along to see how the different apertures change the look of the image.

If you choose to use a smaller aperture (the higher numbers) the subject and background will come more into focus and it will help your image have a long depth of field.

What's depth of field? Well when you take a photograph sometimes you'll notice only parts of the subject you focused on are sharp. This area of sharpness is called the depth of field, and this area extends behind and infront of your subject. When most of the picture is sharp, we say there's lots of depth of field. When only part is sharp, we say depth of field is shallow.

The depth of field is determined by three key factors - the aperture of the lens, the focal length of the lens used, and the distance you are from the subject. Changing these three elements allows you almost complete control over the depth of field in a picture.

There's a simple, direct relationship between aperture and depth of field - the smaller the aperture, the more extensive the depth of field is.

So if you want to keep as much as possible sharp, you should set as small an aperture as possible.

Taken at f/22 so more of the image is in focus.

If you choose a larger aperture (lower number, bigger hole) the background can blur and the focus will be left on the subject.

Taken at f/2 so the background is blurred and your focus is left on the King.

Why would you want this? Well, on the first image, do your eyes focus just on the King to the right of the image? The answer to that is no but as the second image shows, if you use a smaller aperture (bigger hole) the background will be blurred and your eyes are drawn there.

When would you want to use different apertures? Well with subjects such as landscapes, groups, interiors and travel you'll usually want to keep everything sharp so a smaller aperture (higher number) is best. When you use a smaller aperture there's less light going into the lens so the camera's shutter will stay open for longer which can cause camera shake and as a result, your image will blur. Having your camera on a tripod and using the self timer option can help reduce shake.

For general picture-taking, when you want most of the picture to be in focus, you might want to set an aperture of around f/8 to f/11.

For more information on depth of field take a look at this article: Depth of field.

We hope you enjoyed and learned a few things with this article from the ePHOTOzine Academy Series. This is just one part of a 13 part series - to view others follow the links below:

• ePHOTOzine Photography Academy - Part 1: Camera types
• ePHOTOzine Photography Academy - Part 2: Camera lenses
• ePHOTOzine Photography Academy - Part 3: File types
• ePHOTOzine Photography Academy - Part 4: Apertures explained
• ePHOTOzine Photography Academy - Part 5: Shutter Speeds explained
• ePHOTOzine Photography Academy - Part 6:Exposure modes
• ePHOTOzine Photography Academy - Part 7: Metering explained
  
• ePHOTOzine Photography Academy - Part 8: Autofocus explained
• ePHOTOzine Photography Academy - Part 9: Focus Lock
• ePHOTOzine Photography Academy - Part 10: Drive modes
• ePHOTOzine Photography Academy - Part 11: The ISO speed setting
• ePHOTOzine Photography Academy - Part 12: White Balance
• ePHOTOzine Photography Academy - Part 13: Flash modes