What is the circle of confusion and why does it matter?

The circle of confusion (c) is the largest blur disc on the sensor that the eye still perceives as a sharp point in the final print. It scales with sensor size — about 0.029 mm for a full-frame 35 mm sensor, 0.020 mm for APS-C Nikon/Sony, and 0.015 mm for Micro Four Thirds. A smaller c produces a shallower calculated depth of field because the tolerance for blur is tighter. If you use an unusual sensor or medium-format film, enter a custom value: sensor diagonal (mm) divided by 1500 gives a good starting point.

Why does the far limit show infinity?

When the subject distance equals or exceeds the hyperfocal distance H, the denominator of the far-limit formula (H minus s) reaches zero or goes negative, so the far limit is mathematically infinite. In practice this means everything from the near limit all the way to the horizon is acceptably sharp — exactly what you want for landscape photography.

Is depth of field split evenly in front and behind the subject?

No. At typical shooting distances about one-third of the depth of field falls in front of the subject and two-thirds behind it. The tool reports both distances separately and shows the behind/in-front ratio. The split approaches 50/50 only when the subject is very close, and it tips toward the background at longer distances.

How does aperture affect depth of field?

A wider aperture (smaller f-number such as f/1.8) produces a shallower depth of field because more defocus blur is generated outside the plane of focus. Stopping down (larger f-number, such as f/11 or f/16) deepens the depth of field. The hyperfocal distance grows roughly in proportion to the f-number, so doubling the f-number roughly doubles the hyperfocal distance.

What is the hyperfocal distance and how do I use it?

The hyperfocal distance H is the closest focus distance at which depth of field extends from H/2 all the way to infinity. Focusing at exactly H maximises the depth of field for any given lens and aperture combination. Landscape photographers routinely focus at the hyperfocal distance to keep both the foreground and the horizon sharp simultaneously.

How do I solve for aperture given a desired depth of field?

Switch to Find Aperture mode and enter your desired total depth of field along with the focal length and subject distance. The calculator uses numerical bisection to find the exact f-number, then shows the nearest standard f-stop. This is useful when you know the frame you want — for example, keeping a couple sharp from 2 m to 3 m — and need to know which aperture to set.

Depth of Field Calculator

A depth of field (DoF) calculator for photographers that goes beyond a simple lookup table. Enter your sensor format, focal length, f-number and subject distance, and the tool returns the near limit, far limit, total depth of field, in-front / behind split and the hyperfocal distance — all in metres or feet/inches. It also solves in reverse: give it a target DoF and it tells you which aperture, subject distance or focal length achieves it.

How the maths works

Every depth-of-field calculation starts with the hyperfocal distance H, the focus distance at which depth of field extends from H/2 to infinity:

H = f² ÷ (N · c) + f

where f is focal length in millimetres, N is the f-number and c is the circle of confusion — the sensor-format-specific tolerance for blur. Once H is known, the near and far limits for a subject at distance s are:

Near = s(H − f) ÷ (H + s − 2f)

Far = s(H − f) ÷ (H − s)

When s ≥ H the denominator of the far formula becomes zero or negative, meaning the far limit is infinite. Total depth of field is simply Far − Near. The diagram in the tool maps all four distances on a single log-scale axis so the relative proportions are immediately visible.

Worked example — 50 mm portrait lens

Suppose you are shooting a full-frame sensor camera (c = 0.029 mm) with a 50 mm lens at f/2.8, subject at 3 m:

Hyperfocal: H = 50² ÷ (2.8 × 0.029) + 50 ≈ 30,829 mm (30.8 m)
Near limit: 3000 × (30829 − 50) ÷ (30829 + 3000 − 100) ≈ 2,743 mm (2.74 m)
Far limit: 3000 × (30829 − 50) ÷ (30829 − 3000) ≈ 3,321 mm (3.32 m)
Total DoF: 3321 − 2743 = 578 mm (about 58 cm)
In front: 3000 − 2743 = 257 mm · Behind: 3321 − 3000 = 321 mm · ratio ≈ 1.25× more behind

Stop down to f/8 and the DoF grows to roughly 1.8 m, enough to keep both eyes and ears sharp on a three-quarter headshot. Open up to f/1.4 and it collapses to about 16 cm, isolating a single eye.

Focal length	Aperture	Distance	Total DoF
50 mm	f/1.8	3 m	~0.25 m
50 mm	f/2.8	3 m	~0.58 m
50 mm	f/5.6	3 m	~1.18 m
85 mm	f/1.8	5 m	~0.29 m
24 mm	f/8	3 m	~3.2 m

Landscape use-case — hyperfocal focusing

Set a 24 mm lens at f/8 on full frame (H ≈ 2.5 m). Focus at 2.5 m and everything from 1.25 m to infinity is sharp — you can include a rock in the foreground and a mountain on the horizon in the same frame without focus-stacking. The aperture comparison table in the tool shows you every f-stop so you can trade sharpness for diffraction consciously.

Reverse-solve modes

The calculator supports three solve-for directions, each using iterative bisection on the forward formula:

Find aperture — given a desired DoF, the current focal length and subject distance, find the exact f-number (and nearest standard stop).
Find distance — given a desired DoF, the current focal length and aperture, find the subject distance that produces it.
Find focal length — given a desired DoF, a target aperture and subject distance, find the focal length that achieves it.

These modes are particularly useful when planning a shot before the photoshoot: you can lock in a desired subject-to-background separation and the tool tells you exactly what to put on the lens.