Photography is all about capturing light. Cameras are built to measure and capture light. It's that simple. What makes it hard is that cameras need a very specific amount of light. If they don't get enough light then the image they produce is dark. If they get too much light then the image is "blown out" or too bright. It's our job as photographers to make sure the camera sees the perfect amount of light.
To help us with our job, the stop was invented. The stop helps us describe how much light the camera is getting. Increasing by one stop is the same as doubling the amount of light. Decreasing by one stop is the same as halving the amount of light.
Hopefully you know that light is made up of particles. Let's say that your camera is getting 400 particles of light. Yes, that's a gross underestimate of the light particles your camera receives, but I'm told math is easier with smaller numbers. If you increase by one stop then the camera would receive double the amount of light, or 800 particles. If you increase by two stops then the light would be doubled twice and the camera would get 1600 particles of light. Increase 3 stops, 3200 particles. Increase 4 stops, 6400 particles. etc... In the same way, if you decrease by one stop then the camera would receive half the light or 200 particles. Decrease 2 stops, 100 particles. Decrease 3 stops, 50 particles. etc...
That's all a stop is. You can start from anywhere. You could start with 1,434,031 particles of light. If you increased by one stop then you'd have 2,868,062 particles of light. We use this basic idea in all of the exposure controls. Those are, aperture, shutter speed, and ISO. Stay tuned, because those are the topics for my next three blogs.