Color correction gel at 1/4 CTB strength — reduces blue shift without fully neutralizing it. Used for subtle color temperature adjustments between tungsten and daylight sources.
Technical Specifications
1/4 CTB (Color Temperature Blue) shifts the color temperature by +34 Mired, raising Tungsten light from 3200K to approximately 3800K. With Lee Filters, this filter is numbered #203, and with Rosco, it is #3208 "1/4 Blue". Light transmission is 67%, corresponding to a loss of 0.6 stops.
Practical Application in Film
1/4 CTB is typically used for subtle correction of practicals. Desk lamps, wall sconces, and candle-replacement LEDs are given 1/4 CTB to mitigate extreme warmth without losing credibility as "real" light sources.
Workflow & Combinations
1/4 CTB is often combined:
- With ND for window light simulation
- With 1/4 Plus Green for fluorescent matching
- Stacked to 3/8 CTB (1/4 + 1/8) for intermediate values
Comparison with Other 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 Stops |
| Full CTB | +131 | 5600K | 1.8 Stops |
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