Depth of Field (approx.)

This approximation estimates the total depth of field, meaning the near-to-far span that looks sharp enough in a photo. It comes from the geometry of how a lens focuses light: larger apertures (smaller N) and longer focal lengths spread blur more quickly, while stopping down or focusing farther away increases the tolerated range. The circle of confusion c is the maximum blur diameter your eye/viewing conditions will still accept as "sharp," so it sets the sharpness criterion.

Use this when you need a quick estimate of how much of a scene will look acceptably sharp for a given lens, aperture, and focus distance. It is especially useful in portrait, macro, landscape, and product photography when planning whether you need to stop down or focus stack.

• Mixing units without converting consistently, especially using mm for f and c but forgetting that s is in metres
• Treating the result as exact instead of an approximation that depends on the chosen circle of confusion
• Using this formula for very close-focus or extreme wide-angle cases where the approximation can become less reliable