The Number Behind Every Depth-of-Field Calculation

The circle of confusion is the largest blur spot the human eye still reads as a single sharp point, and it’s the hidden constant behind every depth-of-field and hyperfocal distance calculator. Get it wrong and every downstream number — near limit, far limit, hyperfocal distance — shifts with it. This tool lets you calculate it properly instead of trusting a generic default.

Standard Method: Diagonal ÷ Divisor

The quick, widely used approach divides the sensor’s diagonal measurement by a constant, typically somewhere between 1500 and 1730. Lower divisors are more conservative (a stricter standard for sharpness), higher divisors are more permissive. Most depth-of-field calculators bake in one of these values without telling you which.

Custom Method: Print Size and Viewing Distance

For a more precise number, this tool can also derive the circle of confusion from your actual intended output: enter the print diagonal and expected viewing distance, and it works backward through the enlargement factor to the exact blur spot size on the sensor that would still look sharp under those specific viewing conditions.

This tool is especially useful for:

• Photographers printing large who need a circle of confusion matched to their actual output size.
• Anyone cross-checking a depth-of-field calculator’s default assumptions.
• Lens and camera reviewers who need a documented, defensible CoC value for published test charts.