Double CTO

Overview

Double CTO (Double Colour Temperature Orange) is an orange color correction gel (conversion filter) for film lighting. CTO gels convert cool daylight sources into warm artificial light (tungsten) by adding a positive Mired shift to the light color. While a Full CTO brings daylight (approx. 5500–6500 K) down to approximately tungsten level (approx. 3200 K), Double CTO goes significantly further: it is the double-strength version and colors the source far beyond tungsten into a deeply warm, amber range.

The gel is applied as a sheet or from a roll in front of light fixtures, in filter frames, or stretched across windows and skylights. Well-known products include LEE Filters #287 “Double C.T. Orange" and Rosco Cinegel “Double CTO" (#3420). Double CTO therefore belongs to the category of light filters/gels – it is not a light source, not an ANSI lamp code, and not a grip device.

Technical Data

The following values refer to LEE Filters #287 “Double C.T. Orange" according to the manufacturer's specifications:

The Rosco version (Cinegel “Double CTO", #3420) is in a comparable range (Mired shift around +320). For comparison: a Full CTO provides roughly half the Mired shift of a Double CTO. CTO gels are offered in graduated strengths (1/8, 1/4, 1/2, 3/4, Full, and indeed Double), allowing for fine adjustment of correction and warmth effect. They are typically supplied as sheets (approx. 24" x 21") as well as rolls (e.g., 7.62 m x 1.22 m).

On-Set Usage

Double CTO is used when a normal Full CTO does not provide enough warmth – for example, to heavily convert very cold skylight or HMI/LED daylight, or to deliberately create over-corrected, deeply warm looks (sunset, candlelight, or firelight mood). Practically, the gel is also used to make a daylight source appear warmer than the existing tungsten ambient light.

Important for planning: The high Mired shift is accompanied by significant light loss (guideline around 2 stops). Since Mired values are additive, the effect of a Double CTO can also be approximated by combining multiple weaker CTO gels – however, each additional layer further reduces light. With heat from powerful light sources, ensure adequate distance to prevent the gel from fading or burning.