By John Siskin
So last week I tried to explain the concept of a stop. This week we’ll talk about the shutter; among other things we’ll see how stops are used to control the shutter. But first a quick explanation of the shutter in all DSLR cameras and many of the fixed lens cameras the shutter is a physical object that moves over the sensor. It is important to remember this, since it explains some of the limitations of the shutter. There are two curtains on a shutter, one uncovers the sensor and the second covers it up again. Both must move at exactly the same speed for the entire time they are moving over the sensor or your exposure will be uneven. It is really quite amazing how well shutters work, considering the difficulty of the job.
Each full shutter speed is separated by one stop from the one on each side. So if you have a one second shutter speed the speed with one stop less light will be 1/2 second and the speed with one stop more light will be 2 seconds. That makes sense, since as I said last week one stop more light is double the amount of light you had and one stop less is half the amount of light you had. The same principal applies at the higher shutter speeds one stop more light than a 1/250th of a second is a 1/125th of a second and one stop less light is 1/500th of a second. Modern shutters also have 1/2 stop intervals so you would actually see speeds in this order 1/125, 1/180, 1/250, 1/350, 1/500. There might be an advantage in memorizing these numbers, but I don’t know what it would be. It is pretty easy to double or halve a number is you need to know what the full stop change will be.
The change in the shutter speed affects the way the camera sees time. A short shutter speed, say a 1/250th of a second freezes time and a long shutter speed, say a second blurs time together. So for shooting sports you almost always want a high shutter speed to capture the action. If you are shooting waterfalls, you may want to shoot a different shutter speeds in order to get the look you want. Next week I’ll post information about hand holding shutter speeds.
 Tar Creek Falls © John H. Siskin All rights reserved |  Buckhorn Canyon, Angeles Forest, California © John H. Siskin All rights reserved |
 Tar Creek © John H. Siskin All rights reserved |
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