Last Updated 1 hour ago
Filmmaking Dictionary: Number 1 / 1-Stop (One Stop of Exposure)
Definition
One stop is a doubling or halving of an exposure-related quantity. Adding one stop of light exposure doubles it; removing one stop halves it. Stops express a relative change, not a fixed amount of lux or a particular brightness on a monitor.
The term is useful because camera settings and lighting adjustments can be compared on the same scale. However, different ways of changing a stop have different effects on motion blur, depth of field, noise and highlight handling.
Changing Aperture
Opening from f/4 to f/2.8 adds approximately one stop, while closing from f/4 to f/5.6 removes one stop. The f-number changes by approximately the square root of two because light transmission relates to the area of the aperture.
Cinema lenses often use T-stops, which account for measured lens transmission. A one-stop change still represents a factor of two, but an f-number and a T-number do not describe exactly the same lens property.
Advertisement
Other Ways a Stop Changes
- Exposure time: Changing from 1/100 second to 1/50 second doubles the time available to collect light.
- Neutral density: Adding a nominal 0.3 ND removes one stop.
- Illumination: Doubling the light reaching the subject can add one stop of exposure at unchanged camera settings.
- Camera sensitivity setting: A one-stop ISO change affects the exposure interpretation or signal processing; it does not itself put more photons on the sensor.
These changes are not visually interchangeable. A longer exposure time changes motion blur. A wider aperture changes depth of field. An ISO or exposure-index change can behave differently depending on the camera’s recording system.
Example on Set
A face is correctly exposed at T4, but the cinematographer wants T2.8. Opening the lens adds one stop. Adding 0.3 ND removes approximately one stop, keeping the face at roughly the same exposure while permitting the wider aperture.
Similarly, two stops is a factor of four and three stops is a factor of eight. Stop changes add, while the corresponding light factors multiply. This helps crews communicate adjustments without repeatedly converting between percentages.
Common Mistakes
- Calling a one-stop reduction ‘one unit’ of light.
- Assuming every dimmer’s halfway setting removes exactly one stop.
- Treating an ISO change as identical to changing actual illumination.
- Confusing a half-strength diffusion label with half a stop.
Advertisement
Frequently Asked Questions
Is one stop a 50% change?
A one-stop reduction leaves 50% of the starting exposure. A one-stop increase doubles it, which is a 100% increase.
Can a meter show fractions of a stop?
Yes. Third-stop and tenth-stop readings are common, depending on the meter and settings.
Related Terms
Browse all terms starting with 1 or return to the filmmaking dictionary.