Clear protective glass mounted in front of the lens that filters invisible UV radiation and shields the front element from scratches and contamination.
Technical Details
UV filters are made of optical glass with special coatings that absorb or reflect UV radiation. Standard UV filters have a transmission of 85-95% at 400nm, dropping to below 5% at 350nm. The filter strength is indicated in millimeters (usually 2-4mm), with threads following standardized diameters from 37mm to 127mm. UV filters are divided into UV-Haze filters (which additionally block bluish haze) and pure UV filters. Modern multi-coated filters reduce reflections to below 0.5% per surface.
History & Development
UV filters emerged in the 1930s with the widespread adoption of color film material, which was particularly sensitive to UV radiation. Kodak developed the first standardized UV filter for the film industry in 1935. In the 1960s, UV-Haze filters became standard in landscape photography and film production. With the transition to digital cinematography starting in 2000, their importance declined, as digital sensors are significantly less sensitive to UV than analog film material.
Practical Use in Film
In exterior shots at high altitudes or by the sea, where UV radiation is more intense, UV filters prevent bluish color casts and reduced contrast. Classic examples include mountain sequences in "The Sound of Music" (1965) or beach scenes in "Lawrence of Arabia" (1962), where UV filters ensured natural skin tones. Today, the UV filter primarily serves as a protective filter for expensive lenses against dust, saltwater, and mechanical damage. Many DoPs use it continuously as a "protective glass" and only remove it in critical low-light situations.
Comparison & Alternatives
UV filters differ from polarizing filters in their neutral color rendition and from ND filters in their lack of light reduction. Skylight filters (1A/1B) combine UV blocking with slight warming. In digital post-production, UV-related color casts can be corrected afterward, causing UV filters to lose importance. Modern lenses often integrate UV-blocking coatings. Clear filters without UV blocking often serve as pure protective filters today.