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Rosco Roscolux 1/8 CT Blue Lighting Gel - 20x24
Rosco

Rosco Roscolux 1/8 CT Blue Lighting Gel - 20x24"

A 20×24-inch Roscolux 1/8 CT Blue gel that shifts your source approximately 200K cooler — precision color correction in a cut-to-size sheet engineered to survive production heat.

$16.04*
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*Price sourced from Amazon.com. Last updated:Jul 14, 2026.Price and availability are subject to change.

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Overview

The Rosco Roscolux 1/8 CT Blue is a color correction filter designed to introduce a measured, precise cooling shift to tungsten and other warm light sources. In color temperature terms, a 1/8 CT Blue correction sits at the fine-adjustment end of the CTB (Color Temperature Blue) scale — it nudges a source approximately 200K cooler rather than executing the dramatic 2000K shift of a full CTB. This makes it the correct tool for mixed-source color matching scenarios: when one tungsten unit is running visibly warmer than the rest of the package, or when a daylight-balanced camera requires the tungsten sources to move just slightly toward a more neutral rendition without the output sacrifice of a denser correction filter. The high transmission characteristic of the 1/8 density means the footcandle reduction on the corrected fixture is minimal — you refine the color temperature without meaningfully changing the exposure math.

The 20×24-inch sheet format is the production-standard Roscolux cut size — large enough to cover most standard gel frames without cutting, and practical for dividing into multiple smaller pieces for a session requiring consistent correction across several fixtures. Roscolux's material formulation is heat-rated for proximity to tungsten Fresnels, PARs, and HMI sources — it maintains dimensional stability and color consistency through long sessions where cheaper gels warp and shift. In practice, a well-stored Roscolux sheet delivers the same correction at the end of a production day as it did at the first setup, which is the fundamental requirement for a color correction tool in a controlled lighting environment. For gaffers, cinematographers, and stage designers who specify color correction precisely, the Rosco dye standard is the reference point that other gel manufacturers benchmark against.

Key Features

SUPERIOR COLOR ACCURACY - Roscolux filters ensure consistent and precise color correction, maintaining the integrity of your lighting design for professional results every time.

EXCEPTIONAL LIGHT TRANSMISSION - Experience minimal light loss with our 1/8 CT Blue filter, providing optimal brightness and clarity while achieving the desired color effect.

INCREASED DURABILITY & LONGEVITY - Crafted from high-quality materials, Roscolux filters withstand rigorous use, offering extended lifespan and reliable performance in demanding environments.

OPTIMIZED HEAT RESISTANCE - Designed to endure high temperatures from studio lights, preventing warping or color degradation, ensuring consistent results throughout extended shoots.

CONVENIENT SIZE AND SHAPE - The 20x24" rectangular sheet is easy to cut and shape, offering versatility for various lighting setups and creative applications in photography and film.

Specifications

Type
Lighting Gel
Color
1/8 CT Blue
Dimensions
20x24"

Pros & Cons

👍 Pros

  • The 1/8 CT Blue's minimal dye loading produces a subtle 200K cooling shift with very low transmission loss — you correct the color temperature without sacrificing the output level the fixture was balanced for in the exposure plan.
  • The 20×24-inch sheet size cuts efficiently into multiple gel frames or smaller fixture formats from a single purchase, reducing per-fixture cost when correcting several sources to the same color temperature.
  • Roscolux's heat-resistant material formulation survives repeated sessions in close proximity to tungsten and HMI sources without the warping and discoloration that cheaper gels develop after a single session.
  • The precise fractional CT designation allows consistent color correction decisions across multiple fixtures and sessions — repeatable results in a controlled production environment rather than guessing at color shift from unspecified "cool blue" gels.
  • The flat, unperforated sheet format is compatible with gel frames, spring clips, barn door holders, and custom rigging solutions across the full range of production lighting fixtures.

👎 Cons

  • Even with minimal transmission loss, the 1/8 CT Blue absorbs some output — in exposure-critical setups where every stop of output is allocated, the reduction requires compensating with a longer exposure, wider aperture, or higher ISO.
  • The 20×24-inch sheet is a single flat piece with no protective backing — storage and transport require a flat file, gel book, or similar system to prevent creasing, which can cause uneven color across the face of a gel frame.
  • Color temperature correction gels do not correct for spectral quality deficiencies — a tungsten source with poor CRI will render colors inaccurately regardless of whether its color temperature is corrected with a CTB gel.
  • At 1/8 correction strength, the shift is subtle enough that variations in batch-to-batch dye loading may produce slightly different results across separately purchased sheets — this matters in productions where multiple sheets of the same correction are used simultaneously on matched fixtures.
  • The gel will eventually fade and shift color with cumulative heat and UV exposure — in long-run theatrical or installation applications, periodic replacement is required to maintain the original correction value.

Frequently Asked Questions

The 1/8 CT Blue produces approximately 200K of cooling shift — moving a 3200K tungsten source to roughly 3400K, for example. A full CTB shifts approximately 2000K. Use 1/8 CTB when you need to subtly nudge a source toward daylight balance without the significant output loss that a full CTB introduces — common in mixed-source matching where one tungsten fixture runs slightly warm relative to the others.
Roscolux describes the 1/8 CT Blue as providing minimal light loss — its light transmission is high relative to denser correction filters. The fractional CT designation indicates a partial correction, which corresponds to a thinner dye loading in the material and therefore less absorption of the incident light. Precise transmission figures are published in Rosco's filter data sheets for the specific dye batch.
Roscolux gels are formulated for heat resistance from high-output studio and stage fixtures. The 1/8 CT Blue's thinner dye load means it experiences less thermal stress than a denser filter placed at the same distance and wattage. Longevity depends on fixture wattage, distance from the source, and airflow — gels positioned close to high-wattage tungsten sources at zero air gap will degrade faster than those mounted in a gel frame with spacing from the element.
Yes — the 20×24-inch format is a standard sheet size designed to be cut. Scissors or a utility knife cut cleanly along the flat material. The sheet size comfortably accommodates multiple smaller cuts for different fixtures from a single sheet, making it economical for sessions requiring the same correction across several sources.
No — a gel on the source changes the color of the emitted light, affecting the subject, scene, and any reflective surfaces the light touches. A lens filter changes the white balance of everything captured by the camera uniformly. Using gel on a source allows selective correction of individual fixtures while leaving other sources unaffected — a fundamentally different and more precise tool than a camera-side filter.

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