The Basics of Digital Photography: The Exposure Triangle, Part 2

In part 1 of this series, I introduced the new photographer to lens speed, lens aperture, f-stop numbers, depth of field and how they are interrelated. You may want to refresh your memory on what we covered during our last session together by rereading that lesson now. Here's the link to part 1 of this series. In this session we will cover shutters and shutter speed, the second point on our Exposure Triangle. 　

Shutter speed refers to the duration that the lens aperture remains open during the exposure. Shutter speeds vary from one camera to the next. The shutter speeds for the Nikon D40, the available shutter speeds when shooting in the full manual mode ranges from "Bulb" to 1/4000^th of a second. "Bulb" refers to the shutter setting where the shutter remain open for as long as the shutter release remain depressed. These exposures may range from a few seconds in duration to hours. To avoid inducing camera shake during such long exposure a pneumatic bulb release was first used to control the camera shutter, hence the name "Bulb." Later cable releases were introduced. Today we use mostly radio signaling devices to control the shutter during "Bulb" exposures. At the opposite end of the speed range of the D40, the shutter opens and closes in 1/4000^th of one second.

Camera shutters also have another setting that you must understand and that its "Flash Synchronization speed." The Nikon D40 is synchronized to shoot flash photos at any speed of up to 1/500^th second. It's possible to fool a camera into shooting at a faster synch speed than what it's designed to shoot at but that technique is going beyond the scope of this basic photography lesson. Every camera is different so it's very important that you study the manual that came with your camera. With film cameras the shutter speed was selected by adjusting a ring on the lens in the same manner as you turned an f-stop ring to select the desired aperture. In today's digital world, f-stop rings, shutter speed rings, and depth of field charts have disappeared from the lens barrel and reappeared as menu items that's displayed on the camera LCD screen and/or in the viewfinder window. The way you access those menus varies from camera to camera and the way you select shutter speed and aperture varies from camera to camera, the way they interact act are the same.

Just as with lens aperture, the amount of light reaching the film or the sensor in a digital camera is inversely proportional to shutter speed or aperture f-stop. The faster the shutter speed or the larger the f-stop numbers the less the light reaching film or sensor. Shutter speeds like lens aperture change in 1 EV (Exposure Value) steps. This is a very importune concept to master because understanding it allows us to change shutter speeds and apertures at will without having to re-meter the light. For example if you increase the shutter speed one full stop, say from 1/250^th second to 1/500^th second. If the original exposure was f- 5.6 at 1/250^th second you will have to open the lens one full stop to f-4.0 when you increase the shutter speed one full stop to 1/500^th second to maintain the same exposure. Pretty simple once you have the concept fixed firmly in your mind.

Whenever possible keep your shutter speed above 1/60^th of a second because at shutters speeds below 1/60^th of a second it's virtually impossible to shoot with a handheld camera because of camera shake. At speeds below this threshold, you really need to use a tripod or unipod to steady your camera. Personally, I try to not shoot with a shutter speed below 1/125^th second when I'm hand holding the camera.

When selecting a shutter speed you need to keep in mind the effect that you are after. If you are shooting action and you want to stop the action completely, you want to select a fast shutter speed, say 1/500^th second or faster. On the other hand, if you want to introduce some blur in a picture to show movement, choose a slower shutter speed. For example, let say you are shooting a picture of someone standing on a train platform and want to show that the train passing your subject is actually moving fast; shoot at 1/60^th of a second. Your subject will be in perfect focus while the train will be a blur of motion. If your subject is walking on the platform as the train passes, still shoot at 1/60^th of a second but pan with your moving subject to keep them in the center of the frame and in focus. The train will again be a blur of speed and your subject's feet will be slightly blurred to show that they are moving as well. Actually, the best way to learn which shutter speeds work best in any given situation is to experiment. Unlike with film cameras it really doesn't cost you anything but time to experiment when you're shooting digital.

Another important factor to consider when selecting shutter speed is the focal length of the lens. Long lenses, telephoto lenses, are more prone to suffer from camera shake then normal lenses or wide angle lenses are. The longer the focal length the more pronounce the camera shake becomes to the eye.

In part three of this series we will discuss ISO, or sensor sensitivity, how it relates to film speeds, aperture settings, and shutter speeds. Until then take your camera out and practice what we have talked about so far. Set you camera to its "Aperture Priority" mode and experiment with shooting with different f-stops to see how it affects depth of field and focus. Then set your camera to its "Shutter Priority" mode and experiment shooting with different shutter speeds. Remember that in "Aperture Priority" mode, the camera will select the proper shutter speed and when in "Shutter Priority" mode the camera will select the proper aperture.