Lightest CTB color correction filter — reduces yellow cast by ~150K. Subtle correction for slightly warm daylight or studio artificial light sources.
1/8 CTB (Color Temperature Blue) is the weakest level in the CTB family, with a Mired shift of +17. This raises Tungsten light from 3200K to approximately 3500K – a shift perceived visually as a "slight cooling." Lee Filters lists the filter as #218, Rosco as #3216 "1/8 Blue." With 81% transmission, there is a light loss of only 0.3 stops – practically negligible for exposure calculations. Spectral absorption in the red/orange range (580-700nm) is minimal, meaning the filter also barely affects color saturation.
1/8 CTB is primarily used for fine correction and is employed for: LED panels with a color temperature slightly below 3200K (typical for inexpensive Chinese LEDs: 2900-3100K), subtle separation between key and fill light through minimal color contrast, correction of Tungsten practices (bulbs) that become even warmer when dimmed, and as a "safety correction" in unknown mixed lighting situations. Experienced gaffers always carry 1/8 CTB in their gel pouch as it is universally applicable.
1/8 CTB is often combined with other filters: Two layers of 1/8 CTB result in 1/4 CTB (additive Mired shift of +34), three layers achieve 3/8 CTB (+51 Mired). In combination with diffusion (e.g., 1/8 CTB + 216 Diffusion), "Cool Soft Light" is created for beauty shots. For window light, 1/8 CTB is combined with ND to minimally warm daylight without significantly reducing exposure. Its stackability makes 1/8 CTB the most versatile filter in the CTB family.
| Parameter | 1/8 CTB | 1/4 CTB | 1/2 CTB | Full CTB |
|---|---|---|---|---|
| Mired Shift | +17 | +34 | +68 | +131 |
| Kelvin (from 3200K) | 3500K | 3800K | 4500K | 5600K |
| Transmission | 81% | 67% | 52% | 36% |
| Light Loss | 0.3 Stops | 0.6 Stops | 1.0 Stops | 1.8 Stops |
| Lee Filter # | #218 | #203 | #202 | #201 |
| Rosco # | #3216 | #3208 | #3204 | #3202 |
When using 1/8 CTB, consider the following: The filter is so subtle that it is sometimes barely visible on the monitor – vectorscope control is recommended. At temperatures above 200°C, the polyester film can shrink, so keep it away from Fresnel lenses or use heat-resistant variants (Lee HT series). For close-up applications, it is advisable to insert 1/8 CTB film into lamp sockets (E27/E14 compatible sheets). With correct storage (cool, dry, protected from light), the shelf life is 5+ years.
1/8 CTB is my fine-tuning when tungsten light appears minimally too warm, but full or 1/2 CTB would intervene too aggressively. With LED panels that fall slightly below 3200K (some cheaper models are at 3000K), 1/8 CTB brings them back into the standard range. The light loss of 0.3 stops is practically negligible.
In scenes with emotional warmth, I specifically use 1/8 CTB for fill light to increase the contrast between the warm key light and neutral fill. The result is subtle – the audience doesn't consciously perceive it, but the image depth and dimensionality improve noticeably.
1/8 CTB is the most cost-effective correction with hardly any measurable light loss. The minimal filter usage also reduces wear from heat. For long-term series productions with consistent color temperature, I save ND filter budget this way, as I don't have to compensate for CTB light loss additionally.
1. Was beschreibt „1/8 CTB" am besten?
2. Zu welchem Department gehört „1/8 CTB"?
3. Wie viele verschiedene Fachperspektiven bietet dieser Eintrag?
The Lexikon is part of the Filmfarm ecosystem — alongside budgeting (FilmBalance), an industry magazine (FilmCircus) and crew networking (FilmCall, CrewMesh). One shared vocabulary for the whole production.