Support FocalMath

FocalMath is free to use — every calculator and every reference page, no account and no paywall. Keeping it that way costs real money: hosting, the time spent verifying camera specs and formulas, and the ongoing work of adding new reference entries as new cameras ship. If the site has saved you a trip to a forum thread or a mis-metered shot, a small donation helps keep it running and ad-light.

Two Ways to Help

A one-time or recurring donation of any amount, starting at $5, goes directly toward hosting and development. Alternatively, the Field Reference Card Pack is a printable PDF built for photographers who want the site's core numbers — depth-of-field tables for common kits, the NPF astro quick reference, and an exposure-compensation cheat sheet — on paper in a camera bag, for the moments a phone screen is the wrong tool (cold weather, glare, dead battery).

Where the Money Goes

Hosting and domain costs, the ongoing work of keeping camera specs current as new bodies are announced, and time spent adding calculators and reference pages that readers actually ask for. This is a small, focused site, not a large operation — donations make a real, visible difference to what gets built next.

We'll also run a small amount of display advertising to help cover costs without relying on donations alone — you can read exactly what that means for your privacy on the privacy policy page. Between advertising, donations and the paid reference pack, the goal is to keep the core calculators genuinely free and ad-light rather than funding the site through an account paywall or locking any calculator behind a subscription. If you're not in a position to donate or buy the pack, using the site and telling other photographers about it genuinely helps just as much.