Circle of Confusion Explained
The one number hiding inside every depth of field calculation — and the reason calculators disagree with each other.
What is the circle of confusion?
A lens focuses only one plane perfectly. Everything else is a slightly out-of-focus circle of light on the sensor — the "circle of confusion." If that circle is small enough, your eye perceives the point as sharp. The circle of confusion (CoC) is the largest blur spot that still looks like a point in the final print.
Two things decide it: how much you enlarge the image (a full-frame shot printed at 20×24 is enlarged ~8×; a phone shot at the same size is enlarged ~50×) and how close you view from. The classic assumption is an 8×10 print viewed from ~25 cm, which works out to a blur spot of about 1/1000 inch on the print.
The standard values
The most common convention is sensor diagonal ÷ 1500 (some use ÷ 1730 for an even stricter 8×10 standard). ShutterMath uses ÷ 1500 by default. That gives these values:
| Sensor format | Dimensions (mm) | Diagonal (mm) | CoC ÷1500 (mm) |
|---|---|---|---|
| Full frame | 36 × 24 | 43.3 | 0.029 |
| APS-C (Sony / Nikon / Fujifilm) | 23.5 × 15.6 | 28.2 | 0.019 |
| APS-C (Canon) | 22.3 × 14.9 | 26.8 | 0.018 |
| Micro 4/3 | 17.3 × 13 | 21.6 | 0.014 |
| 1-inch | 13.2 × 8.8 | 15.9 | 0.011 |
| Phone main sensor (~1/1.28″) | 9.8 × 7.3 | 12.2 | 0.008 |
Why do calculators give different answers?
- Different CoC standards. Diagonal ÷ 1500 vs ÷ 1730 vs a fixed 0.030 mm for everything vs pixel-based values. The stricter the CoC, the farther the hyperfocal distance and the smaller the depth of field.
- Different sensor dimensions. Some calculators use 36×24 for "full frame" regardless of the camera; exact values (35.9×23.9 for many Nikons) shift results a little.
- Formula variants. Older calculators omit the "+ f" term in the hyperfocal formula — negligible for wide lenses, a few percent for telephotos.
Should you use a stricter CoC?
If you pixel-peep at 100%, or print very large, the classic CoC is too generous. A common stricter choice is diagonal ÷ 2000 (full frame ≈ 0.022 mm). Because H = f²/(N·c), making the CoC one-third smaller makes the hyperfocal distance one-third larger and depth of field roughly one-third smaller. Our depth of field calculator lets you override the CoC — start with ÷2000 if you inspect images closely.
Related guides & tools
Depth of Field Calculator
Try the CoC override and watch near/far limits change live.
Open →Camera Sensor Sizes
Every format side by side with crop factors.
Read →Hyperfocal Distance Chart
Pre-computed values for the standard CoC.
Read →Circle of confusion FAQ
Does my camera's pixel size set the circle of confusion?
Not directly. CoC is about perceived sharpness in the final image, not pixel size. Pixel-based "CoC" values are sometimes used for astrophotography (where a star should ideally land within one pixel), but for general photography the viewing-standard CoC is the right tool.
What CoC does dofmaster or my camera's DoF preview use?
Most classic calculators use diagonal ÷ 1500 (dofmaster lists ~0.029-0.030 mm for full frame). In-camera DoF previews use the lens's actual aperture and the sensor, but the on-screen preview is too small to judge precisely — calculators are more reliable for planning.
Is a smaller CoC always more accurate?
No — it's a threshold, not a measurement. A "stricter" CoC is more conservative (less of the image counts as sharp). Pick the standard that matches how you view: ÷1500 for normal prints, ÷2000 for pixel-peeping and large prints.