Circle of Confusion Calculator
Calculate the circle of confusion (CoC) for any sensor format and viewing distance.
Used for depth of field, hyperfocal distance, and bokeh planning.
Circle of Confusion (CoC)
The circle of confusion is the largest blur circle on the sensor that still appears as a sharp point in the final viewed image. It defines the threshold between “in focus” and “out of focus” for depth-of-field calculations.
Standard Formula
CoC = sensor diagonal / desired enlargement / viewing-distance acuity factor
A common simplification used by camera manufacturers:
CoC = sensor diagonal / 1500
This assumes the print is viewed from a distance equal to its diagonal, by a viewer with normal vision. Smaller sensors → smaller CoC because they need more enlargement to reach the same final print.
Common Standard CoCs
| Sensor | Diagonal (mm) | Standard CoC (mm) |
|---|---|---|
| Full-frame (35mm) | 43.3 | 0.030 |
| APS-C (Nikon / Sony) | 28.3 | 0.020 |
| APS-C (Canon) | 26.8 | 0.018 |
| Micro Four Thirds | 21.6 | 0.015 |
| 1-inch | 15.9 | 0.011 |
| Medium format 645 | 70.0 | 0.047 |
These are the values most DoF calculators and lens manufacturers assume by default.
Why It Matters
Depth of field formulas all use CoC as their tolerance for “acceptably sharp.” A smaller CoC = more demanding sharpness criterion = shallower DoF for the same f-stop. Pixel-peepers viewing 100% crops effectively shrink CoC (sometimes to 1 pixel pitch), which is why DoF “feels” shallower than calculator predictions on high-resolution sensors.
Custom Viewing Conditions
For a specific print size and viewing distance:
CoC = (sensor diagonal / print diagonal) × min_resolvable_size_at_viewing_distance
Standard human visual acuity resolves about 0.2 mm at a 25 cm viewing distance. Scale linearly for other viewing distances.
Worked Example — 8×10 Print at 30 cm
- Print diagonal: 12.8 inches = 325 mm
- Min resolvable at 30 cm: 0.24 mm
- For a full-frame sensor (43.3 mm diagonal): CoC = (43.3 / 325) × 0.24 = 0.032 mm ≈ standard 0.030 mm
Matches the manufacturer default, confirming the standard’s underlying assumptions.
Pixel-Limited CoC
For digital images viewed at 100% on screen:
- 24 MP full-frame: pixel pitch ≈ 6 μm → CoC ≈ 0.012 mm
- 50 MP full-frame: pixel pitch ≈ 4 μm → CoC ≈ 0.008 mm
- 100 MP medium format: pixel pitch ≈ 3.7 μm → CoC ≈ 0.0074 mm
Modern high-resolution sensors push the practical CoC well below the conventional 0.030 mm — leading to noticeably shallower apparent DoF in pixel-peeping conditions.
Caveats
CoC is a viewing-condition-dependent quantity, not an absolute property of the lens. A sharp image at 8×10 may look soft when blown up to 30×40. Always design DoF for the most demanding viewing condition the image will see.
Practical Use
Once you know CoC, plug it into the depth-of-field formula:
DoF ≈ 2 × N × CoC × (focus_distance / focal_length)²
This is what every DoF calculator does internally — and why selecting the right sensor format is the first step in any DoF calculation.