If you’re a regular to Flickr then you’ve probably heard people quoting DOF! Well what’s DOF? DOF stand for depth of field and it’s the main reason why a lot of people will choose to use a Digital SLR. Depth of Field gives you the ability to keep the whole scene in focus or to blur the background (or foreground) of a given subject.
Depth of field is directly related to the aperture that you use within your lens. The aperture is basically the iris within the camera, the wider the aperture, the greater the light that will enter the camera. Aperture can be controlled by using the F-Stop function within the camera or by manually setting the F Stop on the camera lens (not all digital lenses have this function). A wide aperture can provide you deep depth of field, just to confuse matter a wide aperture is the smallest number in F stops that your camera will allow (for example 3.5), where as the smallest aperture will allow that the photograph is sharp from front to back (For example F22).
So if you were wishing to take a portrait you may wish to use a wide aperture. This will ensure that the person in focus will be sharp, but the background will be nicely blurred. If you have a zoom lens then using the top end of the zoom will increase the depth of field available to you, if you have a macro lens you can use the depth of field to even better effect. The photograph below was taken using a very wide angle of 1.8, the focus of the subject was the eye and as I was close in the rest of the child’s face will nicely blur out.
If you were wishing to take a landscape photograph you would use a small aperture (say F22). This would ensure that the photograph would capture all the detail you require. The image below was taken at F25.
Aperture can also be used to good effect to make use of the light that you have available to you. Aperture and depth of field are directly related to the distance that you are away from the subject. Using a wide aperture will allow you to use a much higher shutter speed, where as using a high aperture will lower the shutter speed which may require the use of a tripod. Generally your DSLR will have window on the barrel to show you how far away you need to be from your subject before you start loosing focus.
DSLRS have an aperture priority program (AP) function that will help you control the depth of field by automatically selecting the best shutter speed that is applicable to your selected F stop. This is the easiest way to control depth of field, as you progress you may also wish to go completely manual and control your own shutter speed.
Using the aperture is a great way of taking creative control, each lens has different characteristics so getting out and experimenting is the best way to work out exactly what DOF (see you’re in with the click now!) results you will receive.
One Comment
Great stuff, thanks Mark!
I think the confusing thing about aperture is the F numbers. I think as you say getting out and playing is the best way of working out. Just remember the greater the f-number, the less light enters the camera and the “flatter” it will look.