Free calculator
Depth of Field Calculator
A 50mm lens at f/2.8 focused at 10 ft on Super 35 is sharp from 9.23 ft to 10.9 ft, about 20 inches deep. Enter the lens, stop, distance and format for the near and far limits, the hyperfocal distance, or the focus point and stop that hold two subjects sharp.
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This web tool works out the split-focus stop exactly from the depth of field formulas, so its stop holds both subjects and no more. Save, share and get the Pro tools in the app.
How it works
H = f² ÷ (N × c) + fFocus at H and everything from H ÷ 2 to infinity is acceptably sharp. All lengths in millimeters.
Where
- f
- focal length(mm)
- N
- the stop (f-stop or T-stop)
- c
- circle of confusion, set by the format(mm)
near = s × f² ÷ (f² + N × c × (s − f)) far = s × f² ÷ (f² − N × c × (s − f))Thin-lens limits for a focus distance s, measured from the focal plane. When the far denominator reaches zero, at s = H, the far limit is infinity.
Where
- s
- focus distance(mm)
s = 2 × near × far ÷ (near + far) N = f² × (far − near) ÷ (c × (near + far) × (s − f))Focus at the harmonic mean of the two distances, which always sits nearer the close subject, and set N or deeper. At that focus and stop the near and far limits land exactly on the two subjects.
Choosing the circle of confusion
The circle of confusion is the largest blur that still reads as a point, and the format decides it. The presets are the CineMath app's: Large Format 0.035 mm, Full Frame 0.030 mm, Super 35 0.025 mm, APS-C 0.019 mm, Micro 4/3 0.015 mm, Super 16 0.012 mm. A common rule of thumb divides the frame diagonal by 1,500, which gives 0.029 mm for a 36 × 24 mm frame. Use the diagonal of the area you actually record, and a stricter value for a big screen. The circle of confusion guide has the figures for each format.
How this compares with the CineMath app
The depth of field and hyperfocal figures match the app. For split focus, the app uses a shorter approximation of the stop, (far − near) × f² ÷ (2 × c × s²). It asks for more stop than needed when the subjects are far apart (2 m and 10 m on a 25mm: f/9.0, where f/5.0 holds both) and less than needed close to a long lens (0.5 m and 0.6 m on a 135mm: about 0.8 stop too wide). This page solves the stop exactly from the formulas above.
Worked example
50mm at f/2.8, focused at 10 ft, Super 35 (c = 0.025 mm)
- H = 50² ÷ (2.8 × 0.025) + 50 = 35,764 mm = 117 ft
- s = 10 ft = 3,048 mm; N × c × (s − f) = 0.07 × 2,998 = 209.86
- near = 3,048 × 2,500 ÷ (2,500 + 209.86) = 2,812 mm = 9.23 ft
- far = 3,048 × 2,500 ÷ (2,500 − 209.86) = 3,327 mm = 10.9 ft
Sharp from 9.23 ft to 10.9 ft: 20.3 inches of depth, a little more behind the subject than in front.
Quick reference
Near and far limits at 10 ft, Super 35 (c = 0.025 mm)
| Lens | f/2 | f/2.8 | f/5.6 |
|---|---|---|---|
| 18 mm | 6.81 ft – 18.8 ft | 6.04 ft – 29.0 ft | 4.33 ft – ∞ |
| 25 mm | 8.05 ft – 13.2 ft | 7.47 ft – 15.1 ft | 5.96 ft – 31.0 ft |
| 35 mm | 8.90 ft – 11.4 ft | 8.53 ft – 12.1 ft | 7.44 ft – 15.3 ft |
| 50 mm | 9.43 ft – 10.6 ft | 9.23 ft – 10.9 ft | 8.56 ft – 12.0 ft |
| 85 mm | 9.80 ft – 10.2 ft | 9.72 ft – 10.3 ft | 9.46 ft – 10.6 ft |
| 135 mm | 9.92 ft – 10.1 ft | 9.89 ft – 10.1 ft | 9.78 ft – 10.2 ft |
Hyperfocal distance, Super 35 (c = 0.025 mm)
| Lens | f/2.8 | f/4 | f/5.6 | f/8 |
|---|---|---|---|---|
| 18 mm | 15.2 ft (4.65 m) | 10.7 ft (3.26 m) | 7.65 ft (2.33 m) | 5.37 ft (1.64 m) |
| 25 mm | 29.4 ft (8.95 m) | 20.6 ft (6.28 m) | 14.7 ft (4.49 m) | 10.3 ft (3.15 m) |
| 35 mm | 57.5 ft (17.54 m) | 40.3 ft (12.29 m) | 28.8 ft (8.79 m) | 20.2 ft (6.16 m) |
| 50 mm | 117 ft (35.76 m) | 82.2 ft (25.05 m) | 58.8 ft (17.91 m) | 41.2 ft (12.55 m) |
Save, share and get the Pro tools in the CineMath app
CineMath is a free download for iPhone, iPad and Mac, with this calculator built in. In version 1.3, coming soon to the App Store, CineMath Professional saves calculations to your history, shares them as links, and adds the Camera Database and Data Planning.
Questions
How do I calculate depth of field?
You need the focal length, the stop, the focus distance and a circle of confusion for the format. The near limit is s × f² ÷ (f² + N × c × (s − f)) and the far limit is the same with a minus sign. A 50mm at f/2.8 focused at 10 ft on Super 35 holds 9.23 ft to 10.9 ft.
What circle of confusion should I use?
The format sets it: 0.025 mm is the usual figure for Super 35 and 0.030 mm for full frame, and the calculator offers presets from 0.012 mm for Super 16 to 0.035 mm for large format. A common rule is the frame diagonal divided by 1,500, which gives 0.029 mm for 36 × 24 mm. Use a smaller value if the image will be projected large.
What is the hyperfocal distance?
The focus distance that makes the far limit reach infinity. Focus there and everything from half that distance to infinity is acceptably sharp. On Super 35, an 18mm at f/5.6 has a hyperfocal distance of 7.65 ft, so it holds 3.83 ft to infinity.
How do I keep two subjects in focus?
Choose Split focus and enter both distances. Focus at the harmonic mean, 2 × near × far ÷ (near + far), and set the stop the calculator gives or deeper. For subjects at 6 ft and 10 ft on a 50mm, Super 35, that is 7.50 ft at f/11.2.
Does a bigger sensor give shallower depth of field?
At the same framing and stop, yes. To frame a Super 35 shot on a 50mm, full frame needs about a 72mm lens. At f/2.8 and 10 ft, with each format’s preset circle of confusion, that holds 11.5 inches, against 20.3 inches on Super 35.
Should I enter the f-stop or the T-stop?
Depth of field follows the f-stop, the geometric aperture. A T-stop measures the light the lens actually transmits, so it is a little slower than the f-stop of the same opening. Focus pullers usually work from the T-stop on the barrel; enter the f-stop if you know it and want the exact figure.