Glossary — FocalMath

40 terms that come up across the calculators and reference pages, defined in plain language rather than textbook formality. If a page here uses a term you don't recognize — circle of confusion, pixel pitch, reciprocity failure, whatever it is — this is the fastest place to look it up without leaving the site.

The glossary covers five loose clusters of terms: the core exposure vocabulary (aperture, f-stop, shutter speed, ISO, exposure value, stop of light), depth-of-field vocabulary (depth of field, hyperfocal distance, circle of confusion, focus stacking, focus breathing), sensor and format vocabulary (crop factor, full-frame equivalent, the named sensor formats, aspect ratio), image and resolution vocabulary (megapixel, pixel pitch, dynamic range, raw file, print resolution, DPI versus PPI), and astro-specific vocabulary (the 500 rule, the NPF rule, declination, star trailing, light pollution). Each entry is short and self-contained, with a link out to the deeper explanation — a guide, a calculator, or both — where one exists.

Why a Dedicated Glossary

Photography, like most technical hobbies, accumulates jargon that insiders use casually and newcomers find genuinely confusing — "stop down," "pixel pitch," "reciprocity failure" all mean something specific and useful once explained, but none of them are self-evident from the words alone. Rather than defining every term inline every time it's used across dozens of pages (which would bloat the reference content and risk drifting definitions apart over time), this glossary is the single place each term gets defined once, consistently, and linked to from wherever it's used.

Some entries are genuinely short — a sentence or two is honestly all a term like "ISO" needs once you already understand exposure — and some link out to a full guide because the concept has real depth worth exploring (circle of confusion is the clearest example, since it quietly underlies the entire depth-of-field calculation). The glossary doesn't pad short entries to look more substantial; it says what needs saying and links onward where more is genuinely useful, and stops there rather than inventing extra sentences to hit an arbitrary length or word count that no reader actually asked for.