Stops 101

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When I was new to photography, I was very confused whenever someone said they needed to “stop down” or “stop up” a shot. Basically, all the term “stop” refers to is the change in the brightness of the light, or exposure, of the photograph. Doubling the light is one stop up (or brighter), reducing the light by half is one stop down (or darker).

A “stop” is measured by your camera’s exposure level indicator, which you see when you look into the eyepiece as you’re framing a shot. They’re the numbers -2..1..0..1..2+ (the scale can vary by camera) at the bottom of the viewfinder. Whenever you correctly expose a shot, you’re shooting for the “0″ point in the middle.

Each number is a “stop”, and each “stop” can be divided into thirds before it reaches the next “stop”. That’s why when you hear a professional say, “The shot is just a little too bright and I’m blowing out the whites, so I’m going to stop down by 2/3 of a stop,” the photographer means he or she is going to take the exposure indicator from the “0″ point, to the point just before the “-1″ stop.

Adjusting the exposure’s “stops” apply to shutter, aperture, and ISO interchangeably (though the numbering system is different for each). One can adjust the “stops” by changing any one, or a combination of, these things. For instance, if a shot is composed at a shutter speed of 1/125, aperture f/5.6, ISO 100, it can be “stopped down” one stop by leaving the aperture and ISO the same, but changing the shutter speed to 1/250. Or keep the shutter speed at 1/125 and the ISO at 100, but change the aperture to f/8.0. Or keep the shutter speed at 1/125, the aperture at f/5.6, and change the ISO to 50.

I have found an incredibly handy website tool that visually explains this concept, at Photon Head. I was very excited to find it, I hope you check it out!

Photo Credit: “Old photographic camera with leather cover” by Horia Varlan on Flickr Creative Commons.

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