NZ Photo Info

Depth Of Field or DOF is the part of an image which is in focus. There are a number of different factors that influence the DOF of an image including, focal length, distance from subject and aperture. In this article we will explore aperture.

Aperture is an indication of the size of the opening in the lens on your camera and measured in f-stops or f-numbers. Essentially, aperture is the ratio of the diameter of the opening compared to the focal length of the lens:

• The smaller the f-number the larger the aperture. Resulting in a shallower DOF.
• The larger the f-number the smaller the aperture. Resulting in a larger DOF.

Changing the aperture will also have another affect on your images. By using a larger aperture unless you compensate by slowing down your shutter speed the resultant images will be underexposed or appear very dark. By comparison a small aperture will result in overexposure unless you increase the shutter speed.

If you are using your camera in Aperture Priority mode you won't need to think too much about this. Most Digital SLR's today produce a reasonable result and adjust the shutter speed automatically to suit the conditions.

If you want the greatest control I recommend that you make the decisions rather than letting your camera make them for you. After all, if you are shooting digital you can experiment as much as you want without it costing a fortune.

The below images are examples of the same subject taken at the same time but using different aperture to change the DOF. The focal point was between the P and the U on the lens cover in each photo. Not a very interesting subject but fine for the purpose of this article.

Figure 1: Shallow DOF - Aperture f3.3 - Shutter Speed 1/50sec - Handheld

Figure 2: Larger DOF - Aperture f8 - Shutter Speed 1/20sec - Handheld