1/8 strength CTO filter for minimal daylight-to-warm conversion. Subtle tweak for natural skin tones without heavy color shift.
1/8 CTO (Color Temperature Orange) is the weakest grade in the CTO family with a Mired shift of -17. This lowers daylight from 5600K to approximately 5300K – a shift that is barely perceptible visually but measurable on scopes and colorimeters. Lee Filters lists the filter as #223 ("1/8 C.T. Orange"), Rosco as #3441 ("RoscoSun 1/8 CTO"). With 85% transmission, there is a light loss of only 0.2 stops – negligible for practical purposes.
1/8 CTO is primarily used for fine-tuning and is employed for: HMI lights that are above the 5600K standard (older models, aged bulbs), LED panels with a slightly too cool color temperature (6000K as "Daylight" from some manufacturers), subtle separation between multiple daylight sources in the frame, and as a "safety correction" in unknown mixed lighting situations. Experienced gaffers always carry 1/8 CTO in their gel pouch, as it is universally applicable and causes practically no light loss.
1/8 CTO is often combined with other filters: Two layers of 1/8 CTO result in 1/4 CTO (additive Mired shift of -34), three layers achieve 3/8 CTO (-51 Mired). In combination with diffusion (e.g., 1/8 CTO + 250 Diffusion), minimally warmer soft light is created without noticeable light loss. For window light, 1/8 CTO can be combined with ND to minimally warm and simultaneously dim daylight. Its stackability makes 1/8 CTO the most versatile filter in the CTO family.
| Parameter | 1/8 CTO | 1/8 CTB |
|---|---|---|
| Mired Shift | -17 (warmer) | +17 (cooler) |
| From 5600K | 5300K | 6000K |
| From 3200K | 3100K | 3500K |
| Transmission | 85% | 81% |
| Light Loss | 0.2 Stops | 0.3 Stops |
| Lee Filter # | #223 | #218 |
| Filter | Mired Shift | Kelvin (from 5600K) | Transmission | Light Loss |
|---|---|---|---|---|
| 1/8 CTO | -17 | 5300K | 85% | 0.2 Stops |
| 1/4 CTO | -34 | 4900K | 70% | 0.5 Stops |
| 1/2 CTO | -68 | 4100K | 55% | 0.9 Stops |
| Full CTO | -131 | 3200K | 42% | 1.3 Stops |
When using 1/8 CTO, note: The filter is so subtle that it is practically invisible on the monitor – vectorscope monitoring is recommended. The correction only becomes apparent in a direct A/B comparison or during color grading in post-production. For practical lights (light bulbs in the frame), 1/8 CTO is too weak – use at least 1/4 CTO here. With proper storage (cool, dry, protected from light), its lifespan is 5+ years. For temperatures above 150°C, use heat-resistant HT variants.
1/8 CTO is my fine-tuning when daylight appears minimally too cool, but stronger CTO filters would intervene too obviously. With HMIs that are slightly above 5600K (some older models reach 6000K), 1/8 CTO brings them back into the standard range. The light loss of 0.2 stops is practically unmeasurable.
I use 1/8 CTO for the subtlest of corrections – the audience shouldn't perceive a difference, but should unconsciously get the impression of "warmth." In scenes that are meant to feel emotionally neutral, but not cold, 1/8 CTO on the backlight is often enough to achieve the desired effect.
1/8 CTO is the most cost-effective correction there is – hardly measurable light loss means no bigger lights or generators. On large daylight setups, I save considerably with it, as I achieve the same light output with a slightly warmer look. The filter costs of 8-12 Euros per sheet are negligible.
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