CTO Gel
A colour temperature orange gel that warms a daylight-balanced source to match tungsten light.
Measured in
fraction (¼, ½, full CTO)
In depth
A full CTO shifts flash from about 5600 K down to roughly 3200 K, letting it blend with domestic bulbs so a single white balance renders both correctly. Its blue counterpart, CTB, does the reverse. Partial strengths — quarter and half — are used constantly, because a slight mismatch often looks better than a perfect one.
Examples in practice
A half CTO on a flash matches it closely enough to warm interior lighting that skin tones stay consistent across the frame.