Friday 5 April 2019

exposure - What is one "stop"?



I always hear this term, e.g.,



  • I had to go down one stop

  • Increasing X by Y raises Z by one stop

  • I turned down the flash/the light two stops

  • This lens/sensor/strobe/Photoshop tweak raises X by around one stop


That one too!: "Around one stop"... Is there a 0.85 or a 1.13 of a stop, to be exact?


Is this (always) the same thing as an f-stop? I am so confused!



Answer




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.


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