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Rosco 3208 (1/4 CTB): a light blue color correction gel from Cinegel that slightly converts tungsten light (3200 K) toward daylight temperature (approx. 3500 K).
Overview
Rosco 3208 is a color correction filter (gel) from the manufacturer Rosco's Cinegel series. Its full designation is 3208 Quarter Blue (1/4 CTB) – meaning a quarter blue filter. CTB stands for Color Temperature Blue: filters in this family raise the color temperature of a light source, shifting it from warm artificial light towards cooler daylight.
3208 is one of the weaker grades within Rosco's blue CTB range. The series is tiered by strength of effect – from full correction to very fine fractions: Full Blue (3202), 1/2 CTB (3204), 1/3 CTB (3206), 1/4 CTB (3208), and – even weaker than 3208 – 1/8 CTB (3216). Additionally, there is Double Blue (3220), an over-correcting variant with double the effect. The higher the fractional number, the lower the correction and the higher the light transmission.
Technical Data
The following values are from Rosco product specifications and dealer data sheets:
| Property | Value |
|---|---|
| Designation | 1/4 CTB (Quarter Blue) |
| Series | Rosco Cinegel |
| Color Conversion | Raises approx. 3200 K to approx. 3500 K |
| Light Transmission | approx. 74 % |
| Typical Sheet Size | 20" x 24" (Sheet) |
| Typical Roll Size | 48" x 25 ft |
The filter is deep-dyed and designed to be heat-resistant. However, like all gels, it can deform with prolonged, close use in front of hot light sources.
Set Usage
3208 is used when only a small, fine color temperature correction is desired – for example, to give tungsten sources a slight cool bias without shifting them entirely to daylight. Typical applications:
- Fine-tuning the color temperature of tungsten lights relative to a dominant daylight or HMI source
- Compensating for voltage drop (dimming shifts tungsten towards warm – a slight CTB counteracts this)
- Cooling down aging incandescent lamps or household bulbs
- Subtly boosting aging HMI lights that have drifted warm
Since the correction is small, the light loss is low at around a quarter – one reason why 1/4 filters are popular for fine correction, where a full CTB would cause too much effect and light loss. For even finer adjustments, one would use the next weaker grade, 1/8 CTB (3216).
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