As noted previously, there’s an inverse relationship between aperture and shutter speed. A fast shutter speed does not let in as much light as a slow shutter speed. If you’re using a tight aperture to achieve high depth of field, you will need to use a slower shutter speed (for any given light conditions) than you would while using a wide aperture. Shutter speed is also sometimes called exposure time. It is measured in terms of the amount of time that the camera shutter remains open while taking the picture. A fast shutter speed means a short exposure time, while a slow shutter speed means a long exposure time. (In fact, there is such a thing as “timed exposure” in which the shutter remains open for several seconds in order to photograph something in very poor light or to achieve special effects. This kind of photography is always done using a tripod to stabilize the camera.)

Also as noted previously, a slow shutter speed creates greater effect from camera motion so that a tripod may be required for stability at very slow speeds. However, what matters here is the relative motion of camera and subject. Taking a picture of a moving object with a slow shutter speed can create a blurred image of the object (and the suggestion of motion). Using a faster shutter speed makes the object appear more crisply, with better definition and less blurring. Which of these is desired depends on what effect one wants to create in the image.

Shutter speed is measured in fractions of a second, with standard shutter speeds ranging from 1/1000 of a second to one full second. The shutter, like the diaphragm that controls aperture, is part of the camera body and mechanism, not part of the lens, but in addition shutter speed is set independently of what lens you are using (which is not true of aperture).

The shutter speed and the aperture are inversely related. To properly expose a photo, it’s necessary to have a slower shutter speed the narrower the aperture is set and vice-versa, given any specific combination of lighting conditions and lens speed. Just as it’s possible to have a camera automatically set the shutter speed while maintaining a constant aperture (aperture priority), it’s also possible to maintain a constant shutter speed for a particular effect and vary the aperture automatically instead (shutter speed priority). You could have a very fast shutter speed to capture fast-moving objects with crisp focus, or a slower shutter speed to show the motion of the objects with artful streaks. Your camera would then adjust the aperture to let in more or less light as needed to take a properly-exposed picture given that shutter speed and ambient lighting.

• Black, Brian. DSLR Photography for Beginners: Take 10 Times Better Pictures in 48 Hours or Less! Best Way to Learn Digital Photography, Master Your DSLR Camera & Improve Your Digital SLR Photography Skills