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Filmmaking Dictionary: Number 8 / 80A Colour-Conversion Filter
Definition
An 80A filter is a blue colour-conversion filter commonly used to photograph under approximately 3200K tungsten light with daylight-balanced film. Its nominal conversion raises the colour temperature of the transmitted light toward approximately 5500K.
The filter goes in the camera’s optical path, usually in front of the lens or in a suitable filter holder. It changes the balance of light reaching the recording medium. It is not a diffusion filter and is not intended to soften facial detail.
Exposure Cost
An 80A absorbs a significant amount of light. A common specification is a filter factor of four, corresponding to approximately two stops of exposure compensation. Check the particular filter and the film manufacturer’s guidance rather than assuming every exposure system compensates automatically.
If a handheld meter reading is taken without the filter in its optical path, the filter factor needs to be accounted for. Through-the-lens metering may already include its effect, so adding compensation again can create an exposure error.
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Practical Film Example
A production has daylight-balanced stock but needs to shoot an interior lit primarily by 3200K tungsten fixtures. An 80A can help bring the light reaching the film toward the stock’s intended balance. Its substantial light loss may require more illumination or a wider aperture.
Switching to a suitable tungsten-balanced stock or changing the light sources may be preferable for a particular production. The decision includes exposure, available stock, continuity and the intended look, not simply whether the filter produces the correct nominal conversion.
Mixed Light and Digital Cameras
- The filter affects every source seen through the lens, including any daylight windows.
- It cannot independently balance a tungsten key and a daylight background.
- Digital white balance may provide the desired overall correction without this optical filter.
- A deliberate filtered look should be tested with the actual camera, lighting and grading workflow.
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Frequently Asked Questions
Is 80A the same as CTB gel?
No. They can serve related colour-conversion purposes, but lens filters and lighting gels are different products used in different positions.
Is 80A the same strength as 80B?
No. They are different conversion grades. Identify the source temperature and intended balance before choosing a filter.
Does it increase the light’s brightness?
No. Colour-temperature conversion does not add light; this filter reduces transmission.
Related Terms
- 3200K Colour Temperature
- 5600K Colour Temperature
- CTB (Color Temperature Blue)
- 4″ × 4″ Camera Filter
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