A landscape with a boulder at your feet and a peak on the horizon has to be sharp from front to back, and the only way to know whether it will be is to calculate it. The Depth of field tool does the calculation. This guide explains what the numbers mean and how to use them in the field.
Only one plane is truly in focus. Everything in front of and behind it is slightly blurred, and "sharp" means the blur is smaller than the eye can see in the final print. That threshold is the circle of confusion, and it depends on the sensor size: Lightpath uses 0.030 mm for full frame, 0.020 mm for APS-C and 0.015 mm for Micro Four Thirds — the conventional values for a print viewed at normal distance.
Depth of field gets deeper when you:
It gets shallower when you do the opposite, which is what portrait photographers want and landscape photographers usually do not.
For a given lens and aperture there is one focus distance at which everything from half that distance to infinity is acceptably sharp. That is the hyperfocal distance, and it is the single most useful number in landscape photography:
H = f² ÷ (N × c) + f
with f the focal length, N the f-number and c the circle of confusion. For a 24 mm lens at f/8 on full frame, H ≈ 2.4 m. Focus at 2.4 m and everything from 1.2 m to the horizon is sharp. Focus on the mountain at infinity instead and you throw away the foreground for nothing.
Stopping down past about f/11 on full frame (f/8 on APS-C, f/5.6 on Micro Four Thirds) starts to soften the whole image through diffraction. Depth of field keeps growing but peak sharpness falls. The sweet spot for most landscapes is f/8 to f/11 with the lens focused at the hyperfocal distance. If that still cannot hold a very close foreground, focus-stack two frames rather than shooting f/22.
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