A Depth of Field Example

Control the Range of Photo Sharpness

Guide your viewers' eyes with depth of focus

After reading about depth of field on the Focus Concepts page, you'll still want to see the real impact of aperture on photo sharpness.

Here are three photographs taken from a monitor displaying that page.  In each case, the image was taken with the same camera setup.  Only the aperture and shutter speed changed.

The camera was placed at about a 45 degree angle to the screen in order to get a variation in subject distance - from left margin to right.

To accentuate the depth of field effect in a small area, an effective 300mm focal length lens was used, placed about 20" from the center of the image.

Observe how the amount of legible text increases with each decrease in aperture size.

f 5.6 @ 1/25 s At the lens' widest aperture, depth is shortest - limited to the center of the image.

f 16 @ 1/3 s Reducing the aperture by three stops increases the depth dramatically.  It also creates a corresponding 3 stop increase in shutter speed to compensate for the light lost to the narrower aperture.

f 36 @ 1.6 s Reducing the aperture by another 2-1/3 stops, to the maximum for this lens, increases the depth even more, for maximum clarity.

The top image, with extreme narrow depth of field, has the effect of pulling your eye to the center.  If it strays from center, you feel as if you are at the stage of an eye test where you can clearly decide between "1" and "2". You can see how this works to isolate a subject from its background with this seagull photo.

The middle image still draws your eye to center, but with a less harsh effect.

And, in the last image, the text is easily readable from end-to-end.  But, even at this maximum depth the extreme edges are not crisp.  While this is good enough for readability, it would not be good enough for a landscape with a dramatic boulder in the foreground - you'd want that boulder and the distant trees to be tack sharp.  In that case, you would have to explore backing up from the subject or choosing a wide-angle lens with good depth of field.

For more detail on depth of field, start with this review of a digital photography article by Jim Zuckerman in Shutterbug.