This week I’m going to talk about Depth of Field. Depth of Field (DOF)is the portion of an image that is sharp and in-focus. In photography DOF can be used for many things, particularly in composition. Before I go into its uses there is some terminology that we should clear up first. A wide aperture yields a shallow or small depth of field while a small aperture yields a deep or large depth of field. This seems quite counterintuitive but it has to deal with the part of the lens called the aperture. The aperture is the part of the lens that regulates the light that is allowed to focus on the sensor in your digital camera. A lens’ f/stop is directly related to the aperture. f/1.4 would be considered a low depth of field aperture while an f/stop of f/22 would be considered a high depth of field aperture. Before I get to much more advanced I would just like to say that generally you want to shoot landscape photos around f/11 and low light situations around f/1.8. You will often hear the quality if a lens referred to by its speed. When someone say that the lens is really fast they mean that it has a large aperture/shallow depth of field. Most zoom lens have a varied maximum aperture of f/5.6-3.5 this means that as you increase the focal plane the maximum aperture will vary. If you have expensive lenses that value will be fixed, which for optical reasons is why it costs so much.
From a compositional standpoint, sharpness, clarity, and depth of field all play a roll in conveying a theme or message in photography. With a shallow depth of field (large aperture) you can isolate subject within the image. With a large depth of field (small aperture) you can show extreme depth having both, the main subject and background in focus. Something to also consider is sharpness. Most lens yield the sharpest results at apertures in the middle of it’s minimum and maximum. So achieving the effect you want should take into consideration the acceptable zone or range of sharpness the lens is capable of.
