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The Ins and Outs of High-speed Shutters

Manipulating a camcorder's high-speed shutter is the key to making an inexpensive camcorder act in many ways like a professional camera. Check out how the high-speed shutter works and learn some tricks to successfully use the one on your camcorder.

A camcorder is an artist's tool. Just as a canvas and brush are a painter's implements, a camcorder and tape are what the videographer uses to create art. While painters use paint to create the texture, color and feel of an image, as videographers we use light itself. We increase, decrease, diffuse, bounce and colorize the light we work with. Then we gather it with a lens and focus it onto the camcorder's equivalent of a canvas, the CCD chip (which stands for charge coupled device, if you must know.)

As the light passes into the camera and onto the CCD, there are three main ways to adjust the quantity or intensity of the light. One is through the use of a filter, such as an ND (neutral density) filter or a polarizing filter. Another way is to use the manual iris control of the camcorder lens, if your camcorder has one. The third, shutter speed, is controlled on the CCD chip itself.

High-speed shutter controls can be found on a good portion of consumer camcorders available today. Even a number of inexpensive camcorders have some means of increasing the shutter speed, whether it's on the "sports" setting on the Program AE (autoexposure) dial, or buried in some on-screen menu control.

What many videographers don't know is that this common feature is the key to making an inexpensive camera act in many ways like a professional camera. Learning how to use it is simple. It takes just a short time to grasp all that you need to know in order to start using your camera's high-speed shutter with confidence.

What follows is a series of frequently asked questions we've received on the topic of how to use a camcorder's high-speed shutter. If you have any other questions you'd like to have answered, send them to us (via e-mail or U.S. postal) and we'll see if we can get to them in our In Box column.

What's a Shutter?
On an ordinary window, a shutter is a simple device that opens or closes to control the amount of light (and/or weather) that enters a room. On a film camera, a shutter is a mechanical device that's designed to open for a specific amount of time, in order to let in just enough light to properly expose the film. The principle is the same on a camcorder, but the process is electronic rather than mechanical.

Today, most camcorders use a small silicon chip--the CCD--to gather light. This chip has one face covered with thousands of tiny light-sensitive spots known as pixels (picture elements). Here's how a camcorder works: when light strikes the CCD, each pixel gathers it for a fraction of a second. In this same fraction of a second, the light from each pixel gets measured, quantified, and analyzed for color content. Multiply by the number of pixels (270,000 or more in most cases), then repeat the process once for each field of video (60 times per second), and you begin to appreciate the capabilities of this little silicon wafer.

When you adjust a camcorder's shutter speed, you don't change the number of times per second that the camcorder gathers light. The CCD always gathers light 60 times per second. How long the CCD stays on during those 60 instances each second determines shutter speed. The longer each pixel gathers light, the brighter the signal that gets recorded. Ordinarily, this means that a camcorder's slowest available shutter speed will be 1/60th of a second.

The upper limits of a camcorder's shutter speed, however, are very high indeed. While a shutter speed of 1/500th of a second would be fast for an ordinary film camera's mechanical shutter, many camcorders are available with shutter speeds of 1/10,000th of a second and higher.

Why is Shutter Speed Important?
As we said at the beginning of the article, the videographer's medium is light itself. Anything that allows you to take control of light is useful in helping you to obtain the look that you're after in your video productions.

Two important things happen when you increase shutter speed: the amount of light you gather decreases and moving images become sharper and less blurred. There are other effects to be aware of, but for now it's enough to know that these effects are useful by themselves. If you're going to be shooting in bright conditions, simply increasing the shutter speed is one way to compensate for the overabundance of light. Similarly, if you want each frame of a fast-paced bicycle race or similar high-speed event to be sharp and crisp, go for the highest shutter-speed setting you can.

How do I Control the Shutter Speed?
Unfortunately, most consumer-grade camcorders do not have a direct shutter speed control. Those that do will often have the control selectable via a simple button or an on-screen menu. Typically, one push of the correct combination of buttons will cycle the shutter speed through each of its settings, such as 1/60th, 1/120th, 1/250th, 1/1,000th, 1/2,000th, or something similar.

The good news is that many camcorders that do not have a manual shutter speed control will still have some way to increase or decrease the shutter speed. This usually comes in the form of one of several pre-programmed auto-exposure (AE) settings. The highest shutter speed is typically found in the "sports" autoexposure setting. Some camcorders curiously place the highest shutter speed setting with the digital effects, which is perhaps due to the slightly strobed look that results from using very high shutter speeds.

If you haven't purchased a camcorder yet, or are shopping for a new one, be sure to check to see if it has high-speed shutter controls and look at how each model implements them. Simple switches or programmed autoexposure settings tend to be easier to operate than buried menu commands. Most important is to find a set of controls that works the way that you like best and feel comfortable with.

Can I Use the Shutter Speed to Control the Iris?
Yes. When you adjust the shutter speed on a camcorder that doesn't have manual iris control, you indirectly affect the camcorder's automatic exposure system. If you increase the shutter speed, for example, you will force the auto-exposure system to open up the iris to accommodate for the decrease in brightness.

As you may recall from reading earlier Videomaker technical articles, adjusting the iris has a very important effect on the images you record. As you open up the iris, you decrease the portion of the image that appears in sharp focus. Portrait-style shots, product shots and dream sequences are all examples of video that work well with a shallow depth of field.

Similarly, a decrease in the camera's shutter speed will result in the auto-exposure system closing down the iris to a smaller opening. This creates an increased depth of field, which is useful for shooting landscapes and other static wide-angle shots that don't have much movement in the frame.

Is High-speed Shutter a Special Effect?
Yes, again. Shoot a golf swing at 1/10,000 shutter speed, and you'll see a choppy, strobed-looking effect appearing on the golf club as it arcs over the golfer's head. Golf instructors, for example, often use this setting to identify, evaluate and correct errors in a student's swing.

Ever seen a shot of a bicycle's wheels rotating in reverse as the bicyclist zooms by? Or perhaps how the mag wheels on a car seem to remain still as the car drives by? These effects can also be achieved with a high-speed shutter setting. Here's how it's done: follow your subject as it rolls past you, watching the output on a monitor if possible. Adjust the shutter speed setting and/or the speed of the subject until you begin to see the spokes of the wheel rotating in reverse. For fine-tuning, you'll likely have to adjust the speed of the subject instead of the camcorder, because most camcorders don't have very fine shutter speed controls.

Practice Makes Perfect
To begin experimenting with your shutter speed settings, simply try shooting the same subject with a variety of different shutter speeds. Note the changes in depth of field, exposure, and the slightly "strobed" look that results at higher shutter speeds. To get a little fancier, try a high shutter speed setting in auto-exposure mode (to force a large iris opening), and then manipulate the manual focus controls in order to produce a "rack focus" effect.

If you have a VCR with a good pause function, try viewing still images of the same scene recorded with both a high shutter speed and a more ordinary shutter speed (like 1/60th of a second). Note how much sharper the frame looks when you shoot it with a higher shutter speed.

Most importantly, think of ways you might use these tips and tricks to make your own videos better. Need to throw the background out of focus, but you don't have manual iris control? Try increasing the shutter speed.

Whatever you do, be sure to look for the settings and situations that produce the kind of video that looks good to you. It may be important to learn all the rules, but for truly creative and inspired video, you may find you have to forget them and do what looks and sounds best to you.

Tags:  January 1999
Joe
McCleskey
Fri, 01/01/1999 - 12:00am