What does “one stop” mean in photography?
Asked 9/15/2011
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I often hear photographers say things like “go down one stop,” “raise the flash two stops,” or “this lens gives about one stop more light.” What exactly is a stop? Is it always the same as an f-stop, or can it also apply to shutter speed and ISO? And can stops be fractional, like 1/3 stop or 0.85 stop?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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A stop will halve or double the amount of light, depending on the direction and that could mean the amount of light reaching the sensor or how sensitive the sensor is made to the light that is reaching it.
So, for example, to reduce something a stop, I could go from ISO 800 to ISO 400, or I could go from a 1/500 to 1/1000 shutter speed, or I could change the aperture from f/2.8 to f/4. Going opposite direction on any of these would increase the light by a stop.
An f-stop is the term used to describe the aperture positions on a lens. It's the basis for the more general term of a "stop" when describing the amount of light for the exposure.
Originally by user472. Source · Licensed CC BY-SA 4.0
user472
14y ago
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Generated from our catalog & community — verify before relying on it.
A stop is a relative unit of exposure: changing something by 1 stop means doubling or halving the amount of light (or the effective exposure/sensitivity), depending on direction.
Examples of a 1-stop change:
- shutter speed: 1/100s to 1/50s = +1 stop, 1/100s to 1/200s = -1 stop
- aperture: f/5.6 to f/4 = +1 stop, f/5.6 to f/8 = -1 stop
- ISO: 400 to 800 = +1 stop, 400 to 200 = -1 stop
“f-stop” specifically refers to aperture settings on a lens. The broader term “stop” is used for any exposure change, including aperture, shutter speed, ISO, flash power, or light output.
Yes, stops can absolutely be fractional. Cameras commonly use 1/3-stop or 1/2-stop increments, and you can describe any exact change in stops. For example, +0.85 stop means a bit less than doubling, and +1.13 stops means a bit more than doubling. In general:
factor of change = 2^(stops)
So one stop is not limited to aperture, even though the term comes from f-stops.
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