Friday, July 29, 2011

Photography Basics - Understanding Stops, F/Stops, and EV Steps

This article is an excerpt from my upcoming book, Moving Beyond Point-and-Shoot Photography, The Next Step: Learning to Use a DSLR or Interchangeable Lens Camera by Darrell Young. This book aims to teach new DSLR or ILC camera users how to use their more powerful cameras in a superior fashion and assumes no previous knowledge of any aspect of photography. Look for it in March 2012.

What is a Stop?


The term stop is used in photography to represent a relative change in the amount of light that is allowed into the camera.


If you double the light getting into the camera with any of the exposure controls, you have increased the light by one stop. If you reduce the light by half with any of the controls, you have reduced the light by one stop.


What tends to confuse many at first is that the word stop is often used when referring to three different exposure controls: ISO sensitivity, aperture, and shutter speed. Why? Because all three can manage the light that creates the picture. In other words, all three exposure controls allow more or less light into the camera. Adjusting these controls is referred to as “stopping down” (allowing less light let in) or “stopping up” (allowing more light in).


This is an important word to photographers because it gives us an easy way to describe either letting twice as much or half as much light into the camera. One stop up lets in twice as much light, one stop down lets in half as much light.


The phrase stopping down is used much more often in photography writing than the term stopping up. For whatever reason, you’ll more often hear stopping up called opening up instead. The term stop originated in the use of the aperture, but eventually came to mean letting in more or less light.


However you hear or read it, just remember that changing a setting by one stop up (opening or stopping up) lets in twice as much light; changing by one stop down (stopping down) lets in half as much light.


When you read something like, “Let in an extra stop of light,” that simply means doubling the light. If you read, “Take away a stop of light,” it means, cut the light in half. Basically, the term “stop” is a shortcut way of saying “twice as much,” or “half as much” light volume.


If these last few paragraphs seem repetitive, it was on purpose. This is a very important phrase for you to understand!


F/Stops or stops running from f/2.8 to f/16, in this case managed by the aperture control. Each step down cuts light in half, while each step up doubles the light into the camera. The aperture controls how much light comes into the camera, while the shutter speed controls how long light comes into the camera. The ISO sensitivity setting controls how sensitive to light your camera's imaging sensor is. Those three controls are the backbone of controlling exposure. My upcoming  book explains how to use them all together, in an understandable way.

What is an F/Stop?


There is a similar term used in photography that is related directly to how a lens works: the f/stop. This is the origin of the term stop, which is just a shortened form of f/stop. The word stop can have meaning for any of the controls, where f/stop is limited to the aperture control.


Basically, f/stop means the same thing as the word stop, except that it is related to the physical aperture control on your camera. You could interchange the words f/stop or stop when talking about controlling the light with your camera’s aperture. Saying, “Open up one stop” means the same thing as “Open up one f/stop”—let in twice as much light, and vice versa. So when you read the word f/stop, just remember it means the same thing as stop, except it is directly related to the aperture control of the camera, not the shutter speed or ISO sensitivity.


The word f/stop comes from the good old days of having f/numbers (aperture numbers) on a ring at the back of a lens (e.g., f/3.5, f/5.6, f/8). When you turned the aperture ring in one direction you would let in more light, or in the other direction, less light. Most new cameras control the f/stops with a dial you turn on the camera’s body.

What is an EV Step?

Most camera users manuals will also call a stop by yet another name called EV step. EV stands for exposure value, and an EV step is a doubling or halving of light or the equivalent of one stop. 


Whenever you see the words stop, f/stop, or EV step, just realize that they all basically mean the same thing, a doubling or halving of the amount of light getting into the camera. 

Keep on capturing time...
Darrell Young

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