About FocalMath

FocalMath started from a specific annoyance: every depth-of-field chart I could find online assumed I was shooting full frame, and I wasn't. Converting a full-frame hyperfocal table to Micro Four Thirds in my head, standing on a trail at dusk trying to get a landscape shot before the light went, is exactly the kind of arithmetic that should not require me to pull out a phone calculator and remember a formula.

What This Site Actually Does

Every calculator here takes your real inputs — sensor format, focal length, aperture, subject distance, camera resolution, whatever the specific tool needs — and computes a real answer using published photographic formulas. Nothing is looked up from a rounded-off chart. The depth-of-field and hyperfocal numbers come from the standard thin-lens formulas; the exposure triangle math is ordinary stop arithmetic; the astro shutter-speed limits use both the traditional "500 rule" and the more accurate NPF rule; the crop-factor conversions separate field-of-view equivalence from depth-of-field equivalence, which get conflated more often than they should.

The reference layer underneath the tools — sensor formats, camera bodies, focal lengths, a glossary, curated long-tail answer pages — exists to feed the calculators, not the other way around. If a page here doesn't help you use a calculator faster or understand what a result means, it probably shouldn't exist, and we've tried to hold the site to that rather than padding it out with pages nobody needed.

What We Get Wrong

Circle of confusion is a convention, not a physical constant — this site uses the diagonal/1500 rule of thumb, which is common but not universal, and every sensor page says so explicitly rather than presenting the resulting hyperfocal number as more precise than it actually is. The NPF rule for astro shutter speed is itself a published approximation with slightly different published coefficients depending on the source; we picked one and say which. Camera specs (resolution, sensor dimensions) are drawn from manufacturer-published figures, and pixel pitch is computed from those, not independently measured. If you shoot with equipment where a number here looks off, we'd genuinely like to know — see the contact page.

How the Site Is Built

Every calculator runs entirely in your browser. Nothing you type into a tool — your sensor choice, your focal length, your subject distance — is uploaded, logged, or stored anywhere. The site itself is static: there's no backend generating your results at request time, no account system, and no dependency on an external API to render a page or compute an answer.