Círculo de Confusão por Sensor

Circle of confusion: defining acceptable sharpness

The circle of confusion (CoC), written c, is the largest diameter an out-of-focus point can have on the sensor while still reading as a sharp point in the final print or on screen. How big that is depends on the sensor size and how much you magnify the image. The industry rule of thumb is c = d / 1500, with d being the sensor's diagonal. Some typical numbers: full-frame (24×36 mm, diagonal ~43 mm) → c ≈ 0.030 mm; APS-C → ~0.020 mm; Micro Four Thirds → ~0.015 mm; 1″ → ~0.011 mm; smartphone 1/1.7″ → ~0.005 mm. The CoC feeds straight into depth-of-field and hyperfocal-distance formulas. Smaller sensors carry a smaller CoC, which is why they need wider apertures or closer focus to get shallow DOF.

Applications

DOF and hyperfocal calculations for landscape and macro work, equipment selection (a larger sensor with the same lens gives you shallower DOF), and print scaling. Bigger prints magnify the effective CoC, so an image that looks sharp on screen can reveal blur once it's blown up to wall size.

FAQ

Why is CoC smaller on smaller sensors? The image has to be enlarged more to reach the same final print size, which magnifies any blur along with it, so the original blur has to start out smaller.

Is the d/1500 value an absolute standard? No. Zeiss historically went with d/1730, and some modern references use d/1730 or even d/1000, depending on what they assume about viewing distance and visual acuity.

Does pixel pitch replace CoC? Not when it comes to DOF. Pixel pitch sets the limit for pixel-peeping, whereas CoC is tied to how the image is actually viewed in the end.