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Now, onto today’s blog post!
This comes from Tom McCabe, based out of New Bern, North Carolina. Tom is Coastal Light Photographic Arts, PPNC’s current chairman of the board, and all around great guy who is willing to share his knowledge and insight about photography. (Don’t let the fact that he’s a former Marine worry you. He is approachable, funny, and full of stories.) Tom shares his expertise on depth of field here from a class he taught.
Depth of Field
Perhaps one of the more confusing terms we use in photography is Depth of Field. Simply defined, Depth of Field is the distance between the nearest object in sharp focus and the furthest object in sharp focus. Think of it like this: depth of field is how much of your image is in focus.
One way the Depth of Field is controlled is by the aperture size. The smaller the aperture, the greater the Depth of Field. With each change of the aperture by full f-stops, the Depth of Field will be halved or will double, depending on the direction of the change.
To clarify, a change from f8 to f11 will decrease the aperture size by half, allowing half the light to strike the film plane or the sensor, and will double the Depth of Field. Conversely, a change in the opposite direction, from f8 to f5.6 will allow twice as much light to reach the film plane or sensor, but will reduce the Depth of Field by half.
Focal Length of Lens
Another factor in the Depth of Field is the focal length of the lens. Depth of Field decreases as the focal length increases. Thus, wide angle lenses exhibit an apparent greater Depth of Field than telephoto lenses. Most single lens reflex cameras, whether film or digital, allow several choices for exposure settings. The two that I use more than others are the Av (aperture variable) and Manual.
When viewing a scene, you must make a determination of how much Depth of Field is important to the scene you wish to record. If a greater Depth of Field is important to the image, I recommend using the Av setting and stopping down (decreasing aperture size) as far as necessary to attain the Depth of Field you desire.
Many cameras have a Depth of Field preview setting, allowing you to see the Depth of Field more clearly through the view finder. Choosing the Av setting allows you to control the Depth of field directly and lets the camera decide the shutter speed. This, of course, may require the use of a tripod if the shutter speed is reduced below the free hand comfort level for sharp images.
Portraits & a Shallow Depth of Field
Portraits most often require a shallow Depth of field, as this prevents the background from becoming distracting and drawing attention away from the subject. You can blur the background this way, allowing the viewer to realize, perhaps by a landmark, where the image was taken without the landmark dominating the scene and overwhelming the subject.
Depth of Field is a very important compositional element. I recommend experimenting. Try different uses of the Depth of Field. You’ll see what a useful tool it is for improving your images.
Would you like to see what different depths of field looks like? Drop us a note and let us know…we’re happy to chat more.