The Shutter Priority mode, referred to on your Mode dial as Tv (which stands for “Time Value”), is where you select the shutter speed and the camera adjusts the aperture accordingly. Use this mode to push yourself toward the more advanced modes with your camera. This will allow you an enormous amount of control with your fi nal image.
Before we go any further, let me briefl y explain the mechanics of the camera shutter. The shutter is like a curtain that opens and closes to allow light to hit the sensor. The speed is calculated in seconds and fractions of a second (which is what you will likely use most often), and the longer the shutter stays open the more light will reach the sensor. Using a very fast shutter speed is ideal for capturing fast-moving subjects (think of a football player jumping in the air to receive a pass), while a slow shutter speed can show movement in an image (like creating a soft effect on the water in a fl owing stream or waterfall). These settings are offset by a larger aperture for fast shutter speeds and a smaller aperture for slow shutter speeds.
It’s important to understand that if the shutter speed gets too low you won’t be able to handhold the camera to take the photo. Doing so might introduce “camera shake” in your image, which often makes an image appear out of focus. A good rule of thumb is to keep your shutter speed the same as your lens’s focal length. For example, if you are using a 200mm lens, try to keep the slowest handheld shutter
speed no slower than 1/200 of a second. Because the 7D has a 1.6 crop-factor, the number might be slightly off, but sticking to that basic principle will help you keep your images sharp and free of camera shake.
WHEN TO USE SHUTTER PRIORITY (TV) MODE
- When working with fast-moving subjects where you want to freeze the action (Figure 3.3);
- When you want to emphasize movement in your subject with motion blur (Figure 3.4)
- When you want to create that silky-looking water in a waterfall or stream (Figure 3.5)
As you can see, the subject of your photo usually determines whether or not you will use Tv mode. It is important that you be able to visualize the result of using a particular shutter speed. The great thing about shooting with digital cameras is that you get instant feedback by checking your shot on the LCD screen. But what if you only have one chance to catch the shot? Such is often the case when shooting sporting events. It’s not like you can go ask the quarterback to throw that winning touchdown pass again because your last shot was blurry from a slow shutter speed. This is why it’s important to know what those speeds represent in terms of their capabilities to stop the action and deliver a blur-free shot.
First, let’s examine just how much control you have over the shutter speeds. The 7D has a shutter speed range from 1/8000 of a second all the way up to 30 seconds. With that much latitude, you should have enough control to capture almost any subject. The other thing to think about is that Tv mode is considered a “semiautomatic” mode. This means that you are taking control over one aspect of the total exposure while the camera handles the other. In this instance, you are controlling the shutter speed and the camera is controlling the aperture. This is important, because there will be times that you want to use a particular shutter speed but your lens won’t be able to accommodate your request.
For example, you might encounter this problem when shooting in low-light situations. If you are shooting a fast-moving subject that will blur at a shutter speed slower than 1/125 of a second but your lens’s largest aperture is f/3.5, you might fi nd that the aperture display in your viewfi nder and on the top LCD panel will begin to blink. This is your warning that there won’t be enough light available for the shot—
due to the limitations of the lens—so your picture will be underexposed.
Another case where you might run into this situation is when you are shooting moving water. To get that look of silky, fl owing water, it’s usually necessary to use a shutter speed of at least 1/15 of a second. If your waterfall is in full sunlight, you may get that blinking aperture display once again because the lens you are using only stops down to f/22 at its smallest opening. In this instance, your camera is warning you that you will be overexposing your image. There are workarounds for these problems, which we will discuss later, but it is important to know that there can be limitations when using Tv mode.
SETTING UP AND SHOOTING IN TV MODE
- Turn your camera on and then turn the Mode dial to align the Tv with the indicator line.
- Select your ISO by pressing the ISO button on the top of the camera and then turning the Main dial (the ISO selection will appear in the top LCD Panel).
- Point the camera at your subject and then activate the camera meter by depressing the Shutter button halfway.
- View the exposure information in the bottom area of the viewfi nder or by looking at the top LCD Panel.
- While the meter is activated, use your index fi nger to roll the Main dial left and right to see the changed exposure values. Roll the dial to the right for faster shutter speeds and to the left for slower speeds.
A slow shutter speed refers to leaving the shutter open for a long period of time—like 1/30 of a second or longer. A fast shutter speed means that the shutter is open for a very short period of time—like 1/250 of a second or less.
IMAGE STABILIZATION LENSES
Some Canon lenses come with a feature called Image Stabilization (IS) (Figure 3.6). It’s a mechanism that’s built directly into the lens and helps reduce motion blur due to camera shake when photographing at slower shutter speeds.
If you have this option on your lens, it’s a good idea to leave it turned on when doing any handheld photography. Because the IS mechanism in the lens moves when turned on, you’ll want to turn it off when using a tripod. It could introduce camera shake in
your images if the camera is perfectly still on a tripod, so it is typically only recommended for handheld photography.