I answer lots of questions from participants at my workshops so I thought I would start a series in my blog that lists and answers these.
I will be posting these each week.
Question: What is a stop of light.
Answer: In photography, a "stop" is a widely misunderstood concept, feared by many because it sounds so complicated. However, it's actually very simple: A stop is a doubling or halving of the amount of light let in when taking a photo. For example, if you hear a photographer say he's going to increase his exposure by 1 stop, he simply means he's going to capture twice as much light as on the previous shot.
A stop is a measure of exposure relating to the doubling or halving of the amount of light. The amount of light captured while taking a photo is known as the exposure, and it's affected by three things - the shutter speed, the aperture diameter, and the ISO or film speed. These are all measured using different units, so the concept of "stops" was invented as a convenient way to compare them.