Photography

Photography and cinema math: depth of field and hyperfocal distance from sensor format, crop factor and equivalent focal length, print dimensions from pixels and DPI, aspect ratio scaling, megapixels, exposure value, shutter angle, flash guide number, and horizontal field of view. Bench and homework estimates — lens charts and manufacturer specs may differ slightly.

Depth of field figures rest on an assumption called the circle of confusion — how large a blurred point can be before a viewer perceives it as unsharp. That value depends on sensor size, how big the image is displayed, and viewing distance, so published tables disagree with each other and all of them are approximations. Treat the numbers as a guide for choosing an aperture, not a guarantee of what looks sharp in a large print. Crop factor scales angle of view but not the physical aperture, so an equivalent focal length does not imply equivalent depth of field or light gathering. For print sizing, 300 DPI is the usual standard for prints held in the hand, while large pieces viewed from a distance are perfectly acceptable at far lower resolution.