Circle of Confusion
Calculate CoC from sensor, print size, and viewing distance
How to use Circle of Confusion
- 1Enter the view distance and the size of the image.
- 2Enter the visual acuity (resolution angle, usually 1/1500 ~ 1/2000).
- 3Reads the dispersive circle diameter used for the bathymetric calculation.
CoC Detail
c = view distance x tan (dissolved angle) (convertable to sensor)Fragmentation is the largest blurry circle diameter that the viewer still sees as a point.
It depends on the size of the image and the distance from which it is viewed: a smaller CoC is needed for a larger picture to come closer.
Circle of Confusion is the fuzzy circle ** formed by point light sources when they lose focus**. When this circle is small enough to be invisible in the final output (photo/screen), it is considered "clear" and the critical diameter is "permissible dispersing circle". It is the baseline for bathymetric calculations.
**Standard extrapolation**: Assuming that 8x10 inches (approximately 20x25 cm) of photographs are viewed at a distance of 25 cm, human eye resolution is about 1/1500 rad, the identifiable diameter is about 0.17 mm. The full picture is zooming up to 8x10 approximately 8 times (250 ÷ 30.4 mm diagonal), so the permissible dispersing circle on the sensor = 0.17 ÷ 8 ≈ 0.021 mm. ** The most commonly used simplified formula is "Screen diagonal ÷ 1500"**, full 43.3 ÷ 1500 ≈ 0.029 mm. There was a slight difference in the value taken by different manufacturers (0.025-0.035), but the impact was modest.
| Painting | Sensor Size | CoC（mm） | Equivalent coefficient |
|---|---|---|---|
| All pictures | 36 × 24 mm | 0.029 – 0.030 | 1.0 |
| APS-C | 22.3 × 14.9 mm | 0.018 – 0.019 | 1.6 |
| APS-C (Nikon/Soney) | 23.6 × 15.7 mm | 0.019 – 0.020 | 1.5 |
| M43 | 17.3 × 13 mm | 0.015 | 2.0 |
| 1 inch | 13.2 × 8.8 mm | 0.011 | 2.7 |
| Medium 645 | 56 × 41.5 mm | 0.047 – 0.050 | 0.62 |
| Cellular 1/1.3 in | About 9.8 x 7.3 mm | About 0.008 | About 5-7 |
The standard acceptable dispersing circle value for each painting
Frequently asked questions
COC, how much?
Common defaults: Full drawings 0.03mm, APS-C 0.02mm, M4/3 0.015mm.
Does output size affect COC?
Yes; larger maps require smaller COCs to maintain the same sense of clarity.
Co.C. is the physical spot on the sensor?
It is a derived tolerance, not a sensor physical feature, and is used to drive the bathymetric equation.
Do you want a smaller COC with a high pixel camera?
Depends on the output. The CEC is based on "normal viewing distance and looking at the whole picture." If you are **100% zoom in on the screen** (equivalent to magnifying to a very large size view), you should really use a smaller CoC (recommended to divide by a pixel gain factor such as 60 million pixels for 0.015 mm), at which point the depth of the view will be significantly lighter —** that is why high pixel bodyshots are more likely to be "crystalized" and why high pixels require more sharpness and focus. **Practical filming proposal: take the usual COC, but know that the magnifying examination will be more rigorous and that a few more copies will be taken.
What does coc have to do with pixel size?
They are independent but they interact. The pixel spacing of a full 45 million pixel sensor is about 4.3 μm, while the COC is 30 μm -- so the "clear" decision cuts across about seven pixels, and that's why the depth is gradient rather than mutation. But if the pixel density is very high (e.g. 100 million pixels painted, pixel spacing 3.8 μm), the same COC crosses more pixels and magnifies the view to see more "not sharper" areas. **Simplicit conclusion: the higher the pixels, the higher the focus accuracy, the deeper the actual available view. **