Tip of the Day - Shutter Speed

Tip of the Day - Shutter Speed

Okay, so I wrote the other day that a properly exposed photograph depends upon three adjustable things: aperture, sensor or film sensitivity to light (called ISO or film (sensor) speed), and shutter speed. Today's tip deals with the last of these-- the amount of time that the shutter is open allowing light to stream to the sensor or the film.

Like aperture, the shutter speed you (or your camera) select determines a proper exposure, but it also helps create some of the effects that you've seen in photographs you admire. Maybe you've even hoped to achieve similar effects. Let's talk about how to do that. But first a note about getting the shot at all.

Shutter speed is generally measured in fractions of a second. Most modern cameras have shutter speeds settings from 1 sec to 1/1000 of a second, or faster (we'll deal with the "B" or "bulb" setting in another tip). As I mentioned above, the shutter speed is an indication of how long the shutter is open, allowing light through the aperture. One of the ways, beyond proper exposure, that this number matters has to do with how long the human body can hold really, really still. It might surprise you to learn that we humans aren't really built to hold that still. As the living, breathing organisms that we are, we tend to be always in motion at least a little bit. Try an experiment. Try sitting rock still and then notice how much is really going on in your body. Even when you are trying to be motionless, you are still breathing, your heart is still beating, your muscles are still moving--albeit slightly--to keep you upright. All of these motions contribute to humans not being very good tripods (and though we are technically bipods (or bipeds, or whatever ;-) ), we just don't hold still that well-- at least in terms of what a camera sometimes needs).

If you take notice of how much you move in a second, you might realize that a frame of film or a digital sensor would detect that motion. As hard as we try, most humans can't hold still enough to avoid moving the camera enough to blur a picture taken at about 1/30 of second or slower. As a result, you should try to keep your shutter speed above that number when hand holding your camera. At shutter speeds of 1/60 of a second or faster, the shutter is open so briefly that a little tremor by the photographer will go unnoticed. So, keep your shutter speed above 1/30 most of the time.

What does shutter speed for the image itself, then? The main thing is, of course, that it stops the action-- or doesn't. Take a look at these two images.




The first image depends upon a fast shutter speed to stop the action. Even a sprinting soccer player or a ball that has just been blasted by the kicker can't move very far in 1/1000th of a second. (In this case, the shutter speed was 1/640 and the aperture was f5.6, 300mm lens.)

The second image relies upon a slow shutter speed to give a soft, ethereal quality to the water. This shutter speed was just 1/3rd of a second (f8, 170mm lens). Pretty slow. The water flowing across the rocks becomes blurred and smoothed.

To get your camera to achieve such effects, use the shutter priority mode. That is to say, you select the shutter speed and the camera selects an appropriate aperture (f-stop) if it can. The "sports" mode is essentially a shutter-priority mode that is biased towards faster shutter speeds. A landscape mode, on the other hand, is an aperture-priority mode that favors small apertures (higher f-numbers) to achieve a greater depth of field.

Tip of the Day - Aperture, part 1

I taught a photography mini class not too long ago and I realized in talking to those students that not everyone knows the three basic physical elements that determine the exposure of a photograph: aperture, shutter speed, and ISO. A basic understanding of these three things gives a photographer much more control over what kinds of picture he/she will achieve.

Basically, aperture (also called f-stop) is the size of the hole that lets light through the lens (similar to the pupil of your eye). Shutter speed is how long the shutter is open to let light through that hole. ISO is another term for film speed, which is a measure of a film's (or digital camera's sensor's) sensitivity to light. These three elements combine in many different ways to achieve different results.

Before we discuss how aperture creates story, let's look at how the three elements work together. To achieve a properly exposed photograph (saying nothing, for the moment, about composition or color or anything else) the camera must receive the "right" amount of light on the film or the sensor. Let's call that amount X. Amount X is roughly the same for each ISO setting or film speed. X is equal to 100 for 100 speed film or an ISO setting of 100 on a digital camera (there is some complicated math behind this, if you are interested). Depending upon how much ambient light is available in the scene you are photographing, the photographer (or the camera) adjusts the aperture and shutter speed to get the needed amount of light to the sensor or film.

A large aperture means that lots of light gets through the lens to the sensor at a time. A small aperture means less light gets through at a time. If lots of light gets through quickly, then the shutter does not have to stay open as long. If little light gets through, then a longer shutter speed is needed. Additionally, a sensitive sensor or film means that less light is necessary to achieve the correct exposure. Kind of basic stuff, but, as I said, not understood by some photographers and therefore worth reviewing.

I'll discuss shutter speed and ISO in more detail another day. Today I'm posting about the ways that aperture creates effects on the image you get (or the image you are trying to get). Take a look at part 2 of this tip, which is posted separately.