Cinematographer
1/2 CTB is my workhorse for mixed lighting situations. With a 4500K white balance, I can mix both light sources acceptably. A stop of light loss is calculable.
Mid-strength CTB color correction filter with +68 Mired shift for converting tungsten (3200K) to 4500K.
Technical Specifications
1/2 CTB (Color Temperature Blue) shifts the color temperature by +68 Mireds, raising Tungsten light from 3200K to approximately 4500K. With Lee Filters, this filter is numbered #202 ("Half CTB"), with Rosco it's #3204 ("1/2 Blue"). Light transmission is 52%, corresponding to a loss of 1 stop.
Mixed Light Strategy
4500K lies mathematically between Tungsten (3200K) and Daylight (5600K) on the Mired scale. When white balancing to 4500K, Tungsten appears slightly warm and Daylight slightly cool. This symmetrical deviation is perceived as an acceptable "color depth."
Practical Application
Typical applications:
- Interview setup with window light (5600K) as background
- Corporate videos in office environments with mixed lighting
- Location shoots in apartments with mixed practicals
Comparison of CTB Strengths
| Filter | Mired Shift | Kelvin (from 3200K) | Light Loss |
|---|---|---|---|
| 1/8 CTB | +17 | 3500K | 0.3 Stops |
| 1/4 CTB | +34 | 3800K | 0.6 Stops |
| 1/2 CTB | +68 | 4500K | 1.0 Stop |
| Full CTB | +131 | 5600K | 1.8 Stops |
From the crafts
Perspectives
Director
I use 1/2 CTB for the neutral look – neither obviously warm nor cold. It provides the perfect balance, especially for interview setups with window light.
Producer
1/2 CTB is a compromise between color correction and efficiency. The stop of light loss effectively means half the light output on big setups.
More in the lexikon
Related terms
Test your knowledge
Quiz
1. Zu welchem Department gehört „1/2 CTB (Half Blue)"?
2. Wie viele verschiedene Fachperspektiven bietet dieser Eintrag?