How to use the depth of field calculator
- Enter the focal length of the lens in millimeters, the aperture as an f-number and the distance to the subject in feet or meters.
- Check the circle of confusion. The value in the field is an example for full frame, and you can change it for your sensor or your own standard.
- Read the near limit, the far limit, the total depth of field and the hyperfocal distance.
- Change the aperture or distance to see how the sharp zone grows and shrinks.
Formula
Hyperfocal distance H = f^2 / (N x c) + f
Near limit = s (H - f) / (H + s - 2f)
Far limit = s (H - f) / (H - s), or infinity when s is at or beyond H
f = focal length, N = f-number, c = circle of confusion, s = subject distance (all in the same unit)
These are the standard thin lens approximations. They treat the lens as a single ideal element.
A 50 mm lens at f/2.8
With a 50 mm lens at f/2.8 focused at 10 feet and a circle of confusion of 0.029 mm, the hyperfocal distance is 101.18 feet. The sharp zone runs from 9.11 feet to 11.08 feet, which is 1.97 feet deep.
A 24 mm lens at f/8 focused at 10 meters is beyond its hyperfocal distance of 2.51 meters, so the near limit is 1.99 meters and the far limit is infinity. An 85 mm lens at f/1.8 focused at 2 meters keeps only about 5.5 centimeters sharp, from 1.97 to 2.03 meters.
What the circle of confusion means
A point of light that is out of focus turns into a small disc. The circle of confusion is the largest disc you are willing to call sharp. It depends on the sensor size, how big you print or view the image and how closely you look, so it is a choice and not a physical constant.
The example in the field, 0.029 mm for full frame, comes from dividing the sensor diagonal of about 43 mm by 1500. Smaller sensors use smaller values, for example about 0.018 for APS-C. Use your own standard if you view images large or crop heavily.
Using the numbers in the field
Depth of field grows with a smaller aperture (a larger f-number), a shorter focal length and a longer subject distance. Focusing at the hyperfocal distance makes everything from half that distance to infinity acceptably sharp, which is why landscape photographers use it.
The result is an approximation. Real lenses differ, diffraction softens an image at small apertures, and focusing is never exact, so treat the zone as a guide. For other photo and display math, see the aspect ratio calculator, the image print size and DPI calculator and the TV size and viewing distance calculator.
Assumptions and limits
- The formulas are the thin lens approximation, valid when the subject is farther than the focal length.
- The circle of confusion is an editable example. It is not a fixed standard.
- Diffraction, lens aberrations and focus error are not modeled.
- Use the real focal length printed on the lens, not the 35 mm equivalent.
Frequently asked questions
What is the hyperfocal distance?
It is the focus distance at which the far limit of sharpness reaches infinity. Everything from about half that distance to infinity is then acceptably sharp for your settings.
What circle of confusion should I use?
It is your choice. The default is an example for full frame sensors, and smaller sensors use smaller values. Use a smaller value for a stricter idea of sharp.
Does a smaller aperture increase depth of field?
Yes. A larger f-number gives a deeper zone, up to the point where diffraction starts to soften the image.
Why is the far limit infinity?
When the subject is at or beyond the hyperfocal distance, the thin lens formula has no finite far limit, so the tool shows infinity.