What is a “Stop”?

Now we can answer why we use the word “stop” in talking about exposure.

On old cameras with a manual aperture ring, the aperture numbers are marked on the ring, similarly to the picture show above. On these old lenses, there was a mechanical click, or “stop,” built in to the action of that ring. I believe that this is why we refer to the exposure changes in terms of stops.

Next: How aperture relates to other legs of the Exposure Triangle

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