Normal lenses: These lenses have a focal length of 40mm to 85mm. The lens's curvature is normal, and it produces an angle of view that's similar to the one seen by the human eye. You can use this type of lens for shooting portraits, street photography, and still-life photos.
Telephoto lenses: These lenses have a focal length that's greater than 90mm. They have minimum curvature, which produces a narrow angle of view and causes a scene to be magnified. The greater your focal length, the more magnification you have. Telephoto lenses are great for getting close to the action when you're actually far away. This effect can be useful in photojournalism and sports and wildlife photography.
Wide-angle lenses: These lenses have a focal length of 17mm to 35mm. They have a great deal of curvature and produce very wide angles of view. Your camera can see more of a scene through a wide-angle lens. Try using this type of lens to photograph landscapes, architecture, interiors, and large groups of people.
Fisheye lenses: These lenses have a focal length that's less than 16mm, and they produce an extremely wide angle of view. Fisheye lenses typically are used to create a fun or dramatic look, because elements that are close to the lens appear much larger than elements that are slightly farther from the lens. This look is commonly used in sports photography (skating, climbing, and so on) and in dramatic commercial advertising and high-fashion campaigns.
Savinq time With a zoom lens
Some lenses contain a range of focal lengths so you can shift among them to find the right length for a specific shooting situation. These lenses, which are called zoom lenses, are convenient for scenarios that require you to shoot a variety of subjects from varying distances without wasting any time. After all, changing from one lens to another for one shot and then back again for another is time consuming and a pain.
The drawbacks to zoom lenses are that they're heavy and don't always provide the sharpest quality in an image. Most zoom lenses work better at certain focal lengths than at others. Because they can accommodate so many focal lengths, they drop the ball when it comes to perfecting just one.
I took the three images in Figure 3–1 within a matter of seconds using my 28mm-135mm zoom lens. The zoom lens enabled me to display one scene three different ways and to change my message without moving my camera or changing lenses.
24mm, 1/4 sac, f/11, 50 50mm, 1/4 sac, f/11, 50
Figure 3–1: Three angles of view of one scene taken with a zoom lens.
135mm, 1/4 sac, f/11,50
If you find that you require multiple focal lengths to get the job done, you're wise to purchase a couple zoom lenses. If you have a 24mm-70mm zoom lens and a 70mm-200mm zoom lens, you can cover the wide, normal, and tele-photo ranges with just two lenses. Having this variety in two lenses would be much more convenient than carrying 24mm, 35mm, 50mm, 85mm, 135mm, and 200mm lenses and having to constantly change them as you were shooting.
Exposing your Images Properly
Without exposure, you have no image. And without a well-balanced, thoughtful exposure that takes advantage of the tools you have, your image is less likely to be successful. Digital photography is a recording of light received by your camera's digital sensor. The amount of light that's recorded determines how dark or bright the elements in the image appear.
In an overexposed image, highlights — the brightest areas in the image — are blown out (meaning they provided more light to the sensor than was necessary and the sensor recorded them as white) and lack detail. In an underexposed image, shadow areas are dense (meaning they didn't provide enough light to the sensor and appear to blend together in a dark matter) and lack detail. The best exposure for a scene is one that maintains detail in the highlights without underexposing the shadow areas.
In the following sections, I walk you through the information you need to achieve great exposure for your images. I start off with the basics on aperture, shutter speed, and ISO, and then I move on and show you how to use histograms and light meters to determine exposure.
Taking a closer took at aperture, shutter speed, and ISO
Your camera's digital sensor exposes images based on the following factors:
Aperture: The lens's opening, which you can widen to let in more light or close down to limit the amount of light
Shutter speed: The length of time a camera's shutter is open, which determines the length of an exposure
ISO: The sensitivity level that your digital sensor has to light
Understanding how each of these settings works individually and how they work together maximizes your control over any composition. Even though these factors help control your exposure, each controls other specific aspects of your images as well. So by comprehending what each one is used for, you gain the ability to selectively manipulate your exposure while maintaining control of the other effects that are vital to your message.
Aperture, shutter speed, and ISO are represented in stops — units of light used to measure and control exposure. If you increase your exposure by 1 stop, you're brightening your image and the information on your histogram shifts to the right uniformly in the amount of 1 stop. (Refer to the later section "Using a histogram to check exposure" for more on how a histogram can help you.)
The typical range (ability to capture detail) of a digital sensor is about 6 to 8 stops from black to white. Properly exposing a picture of a gray wall produces an image in which the wall appears gray. If you overexpose a gray wall by 3 stops, it appears white. If you underexpose it by 3 stops, it appears black.
I delve into more detail about aperture, shutter speed, and ISO in the following sections.
Controlling tight With your aperture
Your camera's aperture controls your exposure by determining how much light enters the lens during a given exposure. You set your aperture first when the depth of field (the area of a scene that appears sharp in an image) in your scene is important to your message. Then you can adjust the shutter speed and ISO according to your chosen aperture to get the exposure you're looking for in your image. (For more on depth of field, head to Chapter 7.)
A number known as an f-stop signifies what aperture setting you're using. The higher the number is, the smaller your aperture is and the less light it lets in. Figure 3–2 shows aperture values in 1-stop increments. Each f-stop is roughly
50 percent greater than the one before it. The value doubles every 2 stops. If your camera is set to f/8 and you want to increase your exposure by 1 stop, open the aperture to f/5.6.
In addition to exposure, Figure 3–2: Aperture values in 1-stop increments. aperture also controls
your depth of field. A wider aperture produces a shallow depth of field, meaning that less of your image is sharp. A smaller aperture produces more depth of field and shows a greater area of the scene in focus. Setting your aperture to f/5.6 gives you a somewhat shallow depth of field, and shooting at f/2.8 gives you a very shallow depth of field. An f-stop of f/8 gets you closer to a great depth of field, and f/22 is usually good enough to make a whole landscape appear sharp.