Full CTO

Technical Details

A Full CTO filter has a transmission density of 0.6 and reduces light output by approximately two stops (T-stop loss of 2.0). The filter is made of heat-resistant polyester film with precise color layering, capable of withstanding temperatures up to 120°C. Available in standard sizes from 25x30cm to 120x530cm for large-area lighting. Half-strength variants (1/2 CTO, 1/4 CTO, 1/8 CTO) reduce the color temperature by 1200K, 600K, and 300K respectively.

History & Development

Lee Filters developed the first standardized CTO filters for the film industry in 1971, after cinematographers had experimented with improvised orange filters for years. Lee's "201 Full C.T.Orange" became the industry standard, followed by Rosco's "3407 RoscoSun CTO" in 1978. Modern LED panels with built-in color temperature control have reduced filter usage since 2010, but CTO gels remain indispensable for HMI and Tungsten lights.

Practical Application in Film

Cinematographer Roger Deakins extensively used Full CTO on "Blade Runner 2049" (2017) to match HMI lights to the warm ambient mood for interior scenes. Standard application when mixing daylight through windows with artificial light atmosphere in a room. On "Mad Max: Fury Road" (2015), 18K HMIs with Full CTO filters converted harsh daylight into warm sunset light. The light loss requires correspondingly more powerful lights or higher ISO values.

Comparison & Alternatives

85 filters for cameras correct in the opposite direction (artificial light to daylight sensor), while CTO filters modify the light source itself. CTB filters (Color Temperature Blue) achieve the opposite, increasing the color temperature from 3200K to 5600K. Modern bi-color LED panels with variable color temperature (2700K-6500K) are increasingly replacing filtered Tungsten lights, but do not achieve the light output of large HMI lights with CTO conversion.