Why is it that every detail in a photograph is not acceptably clear and sharp? The area in a photograph, from near to far, which appears to be in sharp focus is called depth of field. The laws of light, physics, and optics dictate that this sharply focused area extends from one-third the distance in front of the point of focus to two-thirds beyond. This range expands as apertures get smaller (higher numbers). Knowing these facts and how to use them give photographers their most creative tool. A skilled photographer will use depth of field to emphasize a portrait subject by limiting the sharpness of a confusing background while a landscape photographer would use a small aperture to enhance the image by having tack sharp details from near to far.
What and Why
This digital photograph was taken by a Nikon D200 camera through a Nikon AF-S Nikkor 200-400mm f/4 lens. It was supported by a Gitzo tripod and a Really Right Stuff ballhead. I wanted the eyes to be sharply focused but the background to be out of focus to make the chipmunk stand out, so I selected an aperture of f/4. With this aperture, the camera computed an exposure with a shutter speed of 1/1000th of a second to freeze the chipmunk’s quick movements based on an ISO of 720 (which the camera selected since it was on “auto ISO” mode).
More Articles by: Steve Guymon, Outdoor Digital Photographer:
Digital Photography Tip: Depth of Field
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Digital Photography Tip: Polarizing Filter
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