Tv: Shutter Priority Mode
Tv mode is what we photographers commonly refer to as Shutter Priority mode. If you dig deep in your manual, you will actually see that Tv stands for "Time Value." I'm not sure who came up with this term, but I can tell you that it wasn't a photographer. In all my years of shooting, I don't ever recall thinking, "Hey, this would be a great situation to use the Time Value mode." However, you don't need to know why it is called Tv mode; the important thing is to know why and when to use it.
Just as with Program mode, Tv mode gives us more freedom to control certain aspects of our photography. In this case, we are talking about shutter speed. The selected shutter speed determines just how long you expose your camera's sensor to light. The longer it remains open, the more time your sensor has to gather light. The shutter speed also, to a large degree, determines how sharp your photographs are. This is different from the image being sharply in focus. One of the major influences on the sharpness of an image is just how sharp it is based on camera shake and the subject's movement. Because a slower shutter speed means that light from your subject is hitting the sensor for a longer period of time, any movement by you or your subject will show up in your photos as blur.
When to Use Shutter Priority (Tv) Mode
- When working with fast-moving subjects where you want to freeze the action (Figure 4.3); much more on this is in Chapter 5
Figure 4.3 Even the fastest of subjects can be frozen with the right shutter speed.
- When you want to emphasize movement in your subject with motion blur (Figure 4.4)
Figure 4.4 Slowing down the shutter speed and following the action conveys a sense of movement in the shot.
- When you want to use a long exposure to gather light over a long period of time (Figure 4.5); more on this is in Chapter 8
Figure 4.5 A long exposure coupled with a steady tripod helped capture this shot of the Antelope Slots.
- When you want to create that silky-looking water in a waterfall (Figure 4.6)
Figure 4.6 Increasing the length of the exposure time gives flowing water a silky look.
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 your subject won't give you a do-over? Such is often the case when shooting sporting events. It's not like you can go ask the quarterback to throw that 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 T1i has a shutter speed range from 1/4000 of a second all the way down 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 find your aperture display in your viewfinder and the rear 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, flowing 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 closes 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 (see Chapter 7), 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 rear 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 viewfinder or by looking at the rear LCD panel.
- While the meter is activated, use your index finger 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.