Densitometers quantify optical density by comparing incident light with transmitted or reflected light. Transmission models read X-ray film, photographic negatives and transparent media, while reflection models assess ink density and print quality. Calibration against certified reference strips keeps readings consistent over time and between operators. Stainless steel and metal housings resist corrosion in processing areas. Clear numerical readouts and simple controls shorten measurement time for technicians. Typical uses include radiography quality control, film processing checks, printing and packaging inspection, and laboratory turbidity and McFarland standard assessment.