Lighting
CTO / CTB Gels
Definition
CTO and CTB gels are filters that correct colour temperature. CTO (Colour Temperature Orange) warms a source, typically bringing 5600 K daylight towards 3200 K tungsten. CTB (Colour Temperature Blue) does the reverse and takes tungsten towards daylight. Both come in fractional strengths (1/8, 1/4, 1/2 and full) for fine adjustment. Every gel reduces light output, and a full CTB can cost more than one stop.
In the field
Mixed sources are matched by gelling the minority type. To blend a few tungsten fixtures into a daylight-balanced room, full CTB goes on the tungsten units, which needs far fewer gels than correcting the whole daylight rig.
Sources
- Rosco, Cinegel 3202 Full Blue (CTB) : conversion de 3200 K vers 5500 K, transmission de 36 % · us.rosco.com
- LEE Filters, 201 Full C.T. Blue : conversion du tungstène (3200 K) vers la lumière du jour (5700 K) · leefilters.com
- LEE Filters, 204 Full C.T. Orange : conversion de la lumière du jour (6500 K) vers le tungstène (3200 K) · leefilters.com
- Wikipédia (pointeur secondaire), Color gel : fractions 1/8, 1/4, 1/2, plein · en.wikipedia.org