Color correction gel that converts daylight (5600K) to tungsten (3200K) light. Available as Full CTS (+131 Mired), Half CTS (+65 Mired), and Quarter CTS (+32 Mired).
Technical Details
CTS gels are available in three standard strengths: Full CTS (Mired value +131), Half CTS (+65 Mired), and Quarter CTS (+32 Mired). Transmission for Full CTS is approximately 85%, with a light loss of 0.7 stops. The 0.1mm thick polyester films are heat-resistant up to 150°C and available in rolls of 61cm or 122cm width. Special variants like Double CTS (+162 Mired) allow for extreme corrections for LED panels with high Kelvin values.
History & Development
Lee Filters developed the first commercial CTS gel (Lee 204) for film production in 1971, after cinematographers had previously used improvised solutions with amber gels. Rosco followed in 1975 with the Cinegel series and standardized Mired values. The introduction of CTB gels (Color Temperature Blue) in 1978 completed the correction system. Modern LED panels began reducing the need for gels from 2010 onwards, but they remain standard for mixed lighting situations.
Practical Use in Film
Roger Deakins used Half CTS on the windows in the apartment scenes in "Blade Runner 2049" (2017) to balance warm evening light against cool LED practicals. A typical workflow: daylight sources are filtered with CTS, while tungsten lamps remain unfiltered – creating uniform 3200K lighting. In "Mad Max: Fury Road," John Seale combined Full CTS with 20K Tungsten Fresnels for a consistent desert atmosphere despite fluctuating daylight conditions.
Comparison & Alternatives
CTB gels (Color Temperature Blue) work in reverse, raising artificial light to daylight levels. Modern bi-color LED panels are increasingly replacing filtered artificial light, as they can be continuously adjusted between 2700K-6500K. ND/CTS combination gels reduce light intensity and color temperature simultaneously. For extreme corrections, dedicated Tungsten LEDs provide better color rendition than heavily filtered daylight LEDs. CTS remains indispensable for window corrections and practicals with fixed color temperatures.