Tv: Shutter Priority Mode
Tv mode is what 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 it wasn't a photographer. 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, which determines how long you expose your camera's sensor to light. The longer it remains open, the more light the sensor gathers. The shutter speed also contributes greatly to how sharp your photographs are. 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 (camera shake) or your subject shows up in your photos as blur.
When to use Shutter Priority (Tv) Mode
- When you want to create that silky-looking water in a waterfall (Figure 4.3)
Figure 4.3 Increasing the length of the exposure time gives flowing water a silky look. [Photo: Hiroyuki uchiyama]
- When you want to use a long exposure to gather light over a long period of time (Figure 4.4); you'll learn more in Chapter 8
Figure 4.4 A long exposure makes this amusement park ride look like a completely different structure. [Photo: Patrick gervais]
- When working with fast-moving subjects where you want to freeze the action (Figure 4.5); Chapter 5 covers this in detail
Figure 4.5 Even the fastest of subjects can be frozen with the right shutter speed. [Photo: Anneliese Voigt]
- When you want to emphasize movement in your subject with motion blur
As you can see, the subject of your photo usually determines whether or not you will use Tv mode. It's 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 G12 has a shutter speed range from 1/4000 of a second all the way down to 15 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 "semi-automatic" mode—you control the shutter speed and the camera chooses a corresponding aperture to achieve a well-exposed image. This is important because there will be times that you want to use a particular shutter speed, but the lens won't be able to accommodate your request.
For example, you might encounter this problem when shooting in low-light situations. Suppose you're shooting a fast-moving subject that blurs at a shutter speed slower than 1/125 of a second. The lens's largest aperture is f/2.8, which might not provide enough available light for the shot and result in an underexposed photo. In that case, that aperture display on the LCD appears orange, and the yellow light near the viewfinder blinks to warn you.
Another case in which 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/8 at its smallest opening. In this instance, your camera is warning 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 turn the Mode dial to Tv.
- Select your ISO by rotating the ISO dial.
- Rotate the Front dial to choose a shutter speed, which appears at the bottom of the LCD. Roll the dial to the right for faster shutter speeds and to the left for slower speeds.
- Point the camera at your subject and then activate the camera meter by pressing the shutter button halfway to preview the exposure.
- Release the button and adjust the Front dial to change the setting.
- Press the shutter button fully when you're ready to shoot.