autofocusing system that’s used during Live View and Movie recording. Don’t worry about what the name means – the important point is that it produces faster, more accurate autofocusing. If you’re interested in learning more, go to the 80D product page at the Canon USA website (www.usa.canon.com), which has a link to a section that explains the technology and lists lenses that support it.
❯❯ Focal length and the crop factor: The focal length of a lens, stated in millimeters, determines the angle of view that the camera can capture and the spatial relationship of objects in the frame. Focal length also affects depth of field, or the distance over which focus appears acceptably sharp.
You can loosely categorize lenses by focal length as follows:
● Wide-angle: Lenses with short focal lengths – generally, anything under 35mm – are known as wide-angle lenses. A wide-angle lens has the visual effect of pushing the subject away from you and making it appear smaller. As a result, you can fit more of the scene into the frame without moving back. Additionally, a wide-angle lens has a large depth of field, which means that both the subject and background objects appear sharp. These characteristics make wide-angle lenses ideal for landscape photography.
● Telephoto: Lenses with focal lengths longer than about 70mm are telephoto lenses. These lenses create the illusion of bringing the subject closer to you, increase the subject’s size in the frame, and produce a short depth of field so that the subject is sharply focused but distant objects are blurry. Telephoto lenses are great for capturing wildlife and other subjects that don’t permit up-close shooting.
● Normal: A focal length in the neighborhood of 35mm to 70mm is considered “normal” – that is, somewhere between a wide-angle and telephoto. This focal length produces the angle of view and depth of field that are appropriate for the kinds of snapshots that most people take.
Figure 1-1 offers an illustration of the difference that focal length makes, showing the same scene captured at 42mm (left image) and 112mm (right image). Of course, the illustration shows just two of countless possibilities, and the question of which focal length best captures a scene depends on your creative goals.
This so-called crop factor varies depending on the camera, which is why the photo industry adopted the 35mm-equivalent measuring stick as a standard. With the 80D, the crop factor is roughly 1.6. So the 18–55mm kit lens, for example, captures the approximate area you would get from a 29–88mm lens on a 35mm film camera. (Multiply the crop factor by the lens focal length to get the actual angle of view.) In Figure 1-2, the red line indicates the image frame area that results from the 1.6 crop factor.
When shopping for a lens, remember this crop factor to make sure that you get the focal length designed for the type of pictures you want to take.
❯❯ Prime versus zoom lenses: A prime lens is a single focal-length lens. With a zoom lens, you get a range of focal lengths in one unit. For example, the kit lens we feature in this book has a focal-length range of 18–55mm.
Why select a lens that offers a single focal length when a zoom lens offers a range of focal lengths? In a word, quality. Because of some lens science we won’t bore you with, you typically see some reduction in picture quality at certain points in the range of a zoom lens. On the flip side, a zoom lens is more convenient than carting around a bag of prime lenses, and many zoom lenses today offer very good image quality.
❯❯ Aperture range: The aperture is an adjustable diaphragm in a lens. By adjusting the aperture size, you can control the amount of light that enters through the lens and strikes the image sensor, thereby controlling exposure. The aperture setting also affects depth of field: A wide-open aperture produces a short depth of field, so the subject is sharply focused but distant objects appear blurry; a narrow aperture produces a long depth of field so that both the subject and distant objects appear sharp.
Chapters 7 and 8 cover these issues in detail. For the purposes of lens shopping, you need to know just a few things.
● Every lens has a specific range of aperture settings. Obviously, the larger that range, the more control you have over exposure and depth of field.
● The larger the maximum aperture, the “faster” the lens. Aperture settings are stated in f-stops, with a lower number meaning a larger aperture. For example, a setting of f/2 results in a more open aperture than f/4. And if you have one lens with a maximum aperture of f/2 and another with a maximum aperture of f/4, the f/2 lens is said to be faster because you can open the aperture wider, thereby allowing more light into the camera and permitting the image to be captured in less time. This not only benefits you in low-light situations but also when photographing action, which requires a fast shutter speed (short exposure time). So, all other things being equal, a faster lens is better.
● With some zoom lenses, the maximum and minimum aperture change as you zoom the lens. For example, when you zoom to a telephoto focal length, you usually can't open the aperture as much as you can at a wide-angle setting. You can buy lenses that maintain the same maximum and minimum aperture throughout the whole zoom lens, but you pay more for this feature.
FIGURE 1-1: Julie used a focal length of 42mm to capture the first image and then zoomed to a focal length of 112mm to capture the second one.
FIGURE 1-2: The 1.6 crop factor produces the angle of view indicated by the red outline.
After studying these issues and narrowing down your choices, finding the right lens in the category you want is just a matter of doing some homework. Study lens reviews in photography magazines and online photography sites to find the best performing lens in your price range.
Whatever lens you choose, follow these steps to attach it to the camera body:
1. Turn the camera off and remove the cap that covers the lens mount on the front of the camera.
2. Remove the cap that covers the back of the lens.
3. Locate the proper lens mounting index on the camera body.
A mounting index is a mark that tells you where to align the lens with the camera body when connecting the two. Your camera has two of these marks, one red and one white, as shown in Figure 1-3.
Which marker you use to align your lens depends on the lens type:
● Canon EF-S lens: The white square is the mounting index.
● Canon EF lens: The red dot is the mounting index.
With a non-Canon lens, check the lens manual for help with this step.
4. Align the mounting index on the lens with the one on the camera.
The lens also has a mounting index. Figure 1-3 shows the one that appears on the 18–55mm EF-S kit lens.
5. Keeping the mounting indexes aligned, position the lens on the camera’s lens mount.
6. Turn the lens clockwise until it clicks into place.
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