What a stop of light is and why photographers talk about it
A stop is a doubling or halving of light. Understanding stops makes every other camera setting easier to balance.
Photographers say things like “open up a stop” or “that filter costs three stops.” A stop is simply a doubling or halving of the light that makes up an exposure.
Stops in each setting
- Shutter speed: 1/500 to 1/250 is one stop more light.
- Aperture: f/5.6 to f/4 is one stop more light.
- ISO: 200 to 400 is one stop brighter.
Why it matters
Because every setting is measured the same way, you can trade one for another. If you need one stop faster shutter speed to freeze motion, you can open the aperture one stop or double the ISO and keep the same exposure.
Thirds of a stop
Most cameras move in thirds: f/4, f/4.5, f/5, f/5.6. Three clicks of the dial equal one stop. Exposure compensation works the same way: +1.0 is one stop brighter.
Stops in the real world
- An ND filter marked ND8 blocks three stops.
- A camera with 14 stops of dynamic range can record detail from deep shadow to bright sky.
- The difference between a shaded patio and full sun can be four or five stops.
Once you think in stops, exposure stops being a mystery and becomes simple arithmetic.
Next: Back-button focus: why many pros separate focusing from the shutter
