Blue correction filters (CTB) shift warm tungsten sources to cool daylight — available in 1/8 through Full CTB strengths.
Definition
Color Temperature Blue (CTB) is a family of color correction filter gels that cool down artificial light, bringing it closer to daylight temperature. CTB filters are essential in film production for matching different light sources.
Classification of the CTB Series
The standard CTB series includes:
- Full CTB: Complete conversion (3200K → 5600K)
- 1/2 CTB: Half strength (3200K → ~4400K)
- 1/4 CTB: Quarter strength (3200K → ~5000K)
- 1/8 CTB: Eighth strength (3200K → ~5300K)
- 1/16 CTB: Sixteenth strength (minimal change)
Practical Application
CTB filters are used for:
- Interior Lighting: Matching artificial light to window or exterior light
- Mixed Lighting Scenes: Harmonizing different light temperatures
- Shooting in Various Rooms: Maintaining consistent color temperature across locations
- Time of Day Correction: Adapting to different lighting conditions
Technical Specifications
- Optical Density: Affects light absorption
- Availability: Gel and glass variants
- Storage: Store in a cool, dry place
- Compatibility: Compatible with all standard filter holders
Manufacturers
Major manufacturers include Lee Filters and Rosco. Both offer compatible, but differently numbered, variants.
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