What’s the difference between the focal plane and depth of field?
Asked 7/7/2013
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I’m trying to understand the difference between the focal plane and depth of field, and how they relate to each other in photography.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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The focal plane is the distance from the camera at which the sharpest focus is attained. Depth of field is the range of distances either side at which the focus is "acceptably sharp".
The "acceptably sharp" part is what causes confusion as you need to make assumptions about viewing distance and visual acuity. For this reason a standard figure for the amount of blur that is acceptable tends to be used. It's thus important to realise that any depth of field numbers are approximate, suitable for comparison (i.e. this setup gives DOF of X meters, this setup gives DOF of Y meters) but the actual range that appears sharp will likely differ.
For lenses which exhibit a defect known as field curvature, the focal plane wont be flat but will curve outward, meaning when photographing something dead flat you could end up with the centre sharp but the corners out of focus.
Tilt-shift lenses allow you to tilt the focal plane relative the camera to better suit the subject (for example tilting the focal plane down would help you get more of the ground in focus).
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
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Generated from our catalog & community — verify before relying on it.
The focal plane is the plane at the subject distance where focus is exact. In simple terms, it’s the distance from the camera where the lens is focused most sharply.
Depth of field is different: it’s the range of distances in front of and behind that focus plane that still look acceptably sharp. So the focal plane is the center of sharpest focus, while depth of field is the zone of acceptable sharpness around it.
A key point is that “acceptably sharp” is not absolute. It depends on assumptions such as viewing size, viewing distance, and human eyesight, so depth-of-field figures are always approximations rather than hard boundaries.
In an ideal lens, the focal plane is flat. In some lenses, optical field curvature can make that plane bend slightly, so focus may not be equally sharp across a perfectly flat subject.
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