1/2 CTS (Half Color Temperature Straw)

kelvin 12 plus green 12 minus green

Lighter straw-colored filter for subtle warm correction — reduces blue content by approx. 1650K instead of full 3200K. Used for fine color balancing between daylight and tungsten sources.

Technical Specifications

Color Temperature Shift:

Shift: approx. 150-200 K towards Tungsten
Mired Value: approx. -50 to -65 Mired
Output Temperature: Fluorescent (approx. 4200-4500 K) is shifted to approx. 3800-4200 K
Additional Components: Magenta/Straw tone for green cast compensation

Optical Properties:

Light Loss: approx. 0.4 to 0.55 f-stops
Transmission: approx. 95-96%
Special Feature: Non-neutral color shift (straw color for fluorescent correction)

Application

The 1/2 CTS filter is specifically used for:

Fluorescent Light Correction: In offices, schools, factories, supermarkets with fluorescent tubes
Mixed Lighting with Fluorescent: Combination of Tungsten and fluorescent light
Sodium Vapor Lamps: CTS also helps neutralize the yellow-green cast here
Studio Setup with Fluorescent Ambient Light: When external sources cannot be controlled
Alternative to Electronic WB: Physical filter for more consistent colors across all takes

Manufacturers & Products

Lee Filters:

Lee 209 (Half CTS) - Standard size 0.5m x 1.22m

Rosco:

Rosco 3204 (CTS 1/2 Strength) - Standard size

Tiffen:

1/2 CTS (available as Cut-Gel)

Arri:

CTS 1/2 (for professional integration)

Practical Tips

CTS vs. CTO: CTO is for Daylight-to-Tungsten correction. CTS is specifically for fluorescent light with its typical green cast. Do not confuse them!
Full CTS vs. 1/2 CTS:

Full CTS (1/1): For a strong green fluorescent cast
1/2 CTS: For more moderate fluorescent situations or when Full CTS appears too yellow

Combination with Green Filters: 1/2 CTS is often combined with a Plus Green or Minus Green to correct the green cast even more precisely:

CTS + Plus Green: When the fluorescent green cast is very dominant
CTS + Minus Green: For finer adjustment

White Balance Setting:

Manual: 4000-4200 K
Preset: Fluorescent mode (if available) + additional filter

Storage: CTS filters can yellow if exposed to direct UV radiation. Store cool and dark.
Practical Sizes: 1/2 CTS is available as

Full-frame filters for large luminaires
Cut gels for spots
Gel rolls for continuous lighting

Measurement: When choosing between Full and 1/2 CTS, a color temperature measurement is helpful (Color Meter). This way, you know exactly which strength you need.

From the crafts

Perspectives

Cinematographer

With 1/2 CTS, you have to consider that this filter not only shifts the temperature but also compensates for color casts. Fluorescent light becomes significantly warmer with CTS and loses its typical green cast. The white balance should be set to around 4000-4200 K. With modern cameras, you can also use the fluorescent-specific WB mode and additionally use a 1/2 CTS filter to achieve even better results.

Gaffer

The 1/2 CTS filter is specifically used in situations where you're working with fluorescent or tube lights. Unlike CTO, which just shifts the color temperature, CTS has a slight straw/yellow-red component that compensates for the green spike from fluorescent lamps. This is essential when you're shooting in offices, schools, or supermarkets where fluorescents are the main light. 1/2 CTS is the weaker version and is used when Full CTS is too warm/too yellow.