Tungsten
Typical tungsten lamp
3,200 K
Full CTO brings a daylight source, such as an HMI, down to this.
TheColours
Fifteen filters on the shelf, from the six 1930s Strand numbers to the correction blues and oranges a film crew carries. Open one to see what it does to a lamp.
WarmRoseBlueGreenCorrectionDiffusion
On theshelf
Colours on screen are close, not exact. The swatch books on the bench are the reference.
Two filters in one frame
Stackingmultiplies
Light through two filters is what both of them let through: the product of the two. Every filter you add makes the beam darker and narrows its colour. Where two colours share nothing, almost nothing gets out.
Drawn here by multiplying the two leaves where they overlap.
Correction
Blue and orange filters that move a lamp's colour temperature, so tungsten and daylight sources match on camera. Often used for the look alone.
Daylight
Nominal daylight
5,400 K
Full CTB pulls a tungsten lamp up toward it.
Grades
Full, half, quarter
1 · ½ · ¼
Both CTB and CTO come in half and quarter strengths for a partial shift.
Second axis
Green to magenta
± G
Correction also runs along a green–magenta axis, at right angles to colour temperature.