gen-define-the-circle-of-confusion-and-give-one-short-worked-exa-d161

Define the circle of confusion and give one short worked example.

# Circle of Confusion The **circle of confusion** (CoC) is the maximum blur spot diameter on the image sensor/film that still appears acceptably sharp to the human eye in the final viewed image. It's a critical concept in determining depth of field. ## Key Points: - Points outside the focused plane project as blur circles, not points - The CoC defines the threshold between "sharp enough" and "visibly blurred" - Typical value: ~0.03mm for full-frame sensors, ~0.02mm for APS-C ## Worked Example: **Question:** A full-frame camera (CoC = 0.03mm) with a 50mm lens at f/2.8 is focused at 3m. What is the depth of field? **Solution:** Using the DoF formulas: **Near limit:** $$D_n = \frac{Df^2}{f^2 + Nc(D-f)} = \frac{3000 \times 50^2}{50^2 + 0.03 \times 2.8 \times (3000-50)}$$ $$D_n = \frac{7,500,000}{2500 + 248.2} = 2.73\text{m}$$ **Far limit:** $$D_f = \frac{Df^2}{f^2 - Nc(D-f)} = \frac{7,500,000}{2500 - 248.2} = 3.33\text{m}$$ **Depth of Field = 3.33 - 2.73 = 0.60m (60cm)** *Without the CoC concept, we couldn't quantify what "acceptably sharp" means!*