The Jupiter F-21 is a Soviet-era subminiature camera designed for covert photography, often referred to as a "button camera" because it was built to be concealed inside a coat with the lens disguised behind a false button. It uses a cassette-loaded strip of film and a clockwork spring-wind mechanism, and was produced primarily for state security use rather than the consumer market.

At UK auction today the Jupiter F-21 has a limited but clear track record, with hammer prices ranging from about £180 to £340 and a midpoint around £260 — these are saleroom results, so what a clean example is worth at wholesale rather than a dealer retail price. Completeness drives value: outfits that include the button-front trigger cable, spare cassettes and original case tend to sell for more than a bare body, while rough or seized examples fetch less.