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Photography

Understanding Aperture and Depth of Field


Depth of Field and Aperture Explained.

Understanding Aperture and Depth of Field

by Mark Boardman

December 13, 2018


One of the keys to taking a good photograph is deciding which areas of the image should be sharp and in focus and which should be out of focus. The sharp part of the image is known as the Depth of Field (DOF) and depends on the aperture, the distance between the camera and the subject and the focal length of the lens.

Here I'll share a few tips with you to help understand the relationship between DOF and photographic creativity.

  • DOF is the amount of stuff that is in focus in front of and behind the point on the image that you are focussing on.
  • So for portraits, you want a small DOF where the background is blurred and the subject is sharp, leaping out of the image at you, whereas for a landscape you want a big DOF so that everything is in focus and the viewer can travel throughout the shot.
  • Aperture is a variable size hole inside your lens defined by f numbers, the larger the f-number (or ‘f-stop’), the smaller the hole and the greater the depth of field.
  • To make this easy a small f-number has a small depth of field (smaller area in focus). A large f-number has a large depth of field (a larger area in focus)!
  • Ranges of f numbers vary depending on the type of lens you have from around 1 up to about 40.
  • Be aware that large f numbers (so small aperture holes) can result in slow shutter speeds to allow enough light in so it is important to use a tripod or steady surface to prevent any camera shake and blurring.
  • Therefore you can use depth of field to give context to your photographs, blurring out distracting backgrounds and isolating the details you want in focus, so the viewer is directed around the image in a journey of your choosing.
  • Your camera’s ‘Landscape’ mode is telling the camera to pick a large DOF whereas a ‘Portrait’ mode is telling it to use a small DOF
  • The area ‘in focus’ in your depth of field is approximately 1 third in front of the focus point and two thirds behind, rather than being even front and back. So for a landscape scene try and focus roughly 1 third of the way into your shot to maximise your depth of field.

When looking through a viewfinder in your DSLR the DOF won’t change as you change your aperture, it isn’t until you take the shot that the aperture is applied, so it is important to review your photos as you take them to ensure you are correctly focusing with the right DOF. However many cameras have a depth of field preview button on them (check your user manual – on my Nikon D7100 it’s on the front right of the camera next to the lens marked ‘Pv’). This button will let you see exactly what will appear in focus.

Depth of field

So, go outside and take two photos of the same subject. Use a large depth of field (high f-number) for one and a small depth (small f-number) for the other. Compare the two photos and you will see that the larger f-number has much more of the image in focus, whereas the small DOF will have blurred out the background and kept your subject in focus. Experiment with different f stops and subjects, keep practicing and as you become more familiar with the effect of aperture your work will become more creative and targeted.

And once you have taken your photo Tweet it to us @ThePhotoHour (#ThePhotoHour) or to @StormHour for weather and landscape shots!

And while you're here why not check out our December Weather Photo Favourites - some of the fantastic photos sent to us recently, and see if you can spot good use of Depth of Field!








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