Читать книгу Canon EOS 80D For Dummies - King Julie Adair - Страница 5

One of the biggest differences between a point-and-shoot camera and a dSLR (digital single lens reflex) camera is the lens. With a dSLR, you can change lenses to suit different photographic needs, going from an extreme close-up lens to a super-long telephoto, for example. In addition, a dSLR lens has a focusing ring that gives you the option of focusing manually instead of relying on the camera’s autofocus mechanism.

We don’t have room in this book to go into detail about the science of lenses, nor do we think that an in-depth knowledge of the subject is terribly important to your photographic success. But the next few sections offer advice that may help when you’re shopping for lenses, figuring out whether the lenses you inherited from Uncle Ted or found on eBay will work with your 80D, and taking the steps involved in actually mounting and using a lens.

Choosing a lens

To decide which lens is the best partner for your camera, start by considering these factors:

❯❯ Lens compatibility: Your camera accepts two categories of Canon lenses: those with an EF-S design and those with a plain old EF design.

The EF stands for electro focus; the S stands for short back focus. And that simply means the rear element of the lens is closer to the sensor than with an EF lens. And no, you don’t need to remember what the abbreviation stands for. Just make sure if you buy a Canon lens other than one of the two sold as a bundle with the camera, that it carries either the EF or EF-S specification. If you want to buy a non-Canon lens, check the lens manufacturer’s website to find out which lenses work with your camera.

Two other lens acronyms to note: First, the 18–55mm and 18–135mm lenses that you can buy as part of a 80D kit are IS lenses, which means that they offer image stabilization, a feature you can explore a few sections from here. Second, they also carry another designation: STM (for the 18-55mm lens) or USM (on the 18-135mm lens). The STM abbreviation refers to the fact that the autofocusing system uses stepping motor technology, which is designed to provide smoother, quieter autofocusing. USM stands for UltraSonic Motor, which offers fast, professional-grade autofocusing.

Finally, be aware that, unlike both of the kit lenses available with the 80D, some lenses can’t take full advantage of the Dual Pixel CMOS (see-moss) 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.

Note, however, that the focal lengths stated in this book are so-called 35mm equivalent focal lengths. Here’s the deal: When you put a standard lens on most dSLR cameras, including your 80D, the available frame area is reduced, as if you took a picture on a camera that uses 35mm film negatives and then cropped it.

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.

Attaching and removing a lens

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.

In other words, turn the lens toward the lens-release button, labeled in Figure 1-3.

FIGURE 1-3: Place the lens in the lens mount with the mounting indexes aligned.

To remove a lens, turn the camera off, press the lens-release button, grip the rear collar of the lens, and turn the lens toward the shutter button side of the camera. When you feel the lens release from the mount, lift the lens off the camera. Place the rear protective cap onto the back of the lens, and if you aren’t putting another lens on the camera, cover the lens mount with its protective cap, too.

Always switch lenses in a clean environment to reduce the risk of getting dust and dirt inside the camera or lens. For added safety, point the camera slightly down when performing this maneuver to help prevent flotsam in the air from being drawn into the camera by gravity.

Zooming in and out

If you bought a zoom lens, it sports a zoom ring. Figure 1-4 shows you the location of the zoom ring on the 18–55mm kit lens; for other lenses, see your lens user guide. With the kit lens, rotate the zoom ring to zoom in and out. A few zoom lenses use a push-pull motion to zoom instead.

FIGURE 1-4: Here’s a look at the 18–55mm kit lens.

The numbers around the edge of the zoom ring, by the way, represent focal lengths. The number that’s aligned with the white focal-length indicator, labeled in Figure 1-4, represents the current focal length.

Some lenses, including the alternate 18–135mm kit lens, also have a zoom ring lock switch. When the lens is set to the 18mm position, you can use the switch to lock the lens at that focal length. That way, when the camera is pointing downward, gravity can’t cause the lens to extend to a longer focal length (a problem known as lens creep).

Using an IS (image stabilizer) lens

Both kit lenses sold with the 80D offer image stabilization, indicated by the initials IS in the lens name. Image stabilization attempts to compensate for small amounts of camera shake that are common when photographers handhold their cameras and use a slow shutter speed, a lens with a long focal length, or both. Camera shake can result in blurry images, even when your focus is dead-on. Although image stabilization can’t work miracles, it enables most people to capture sharp handheld shots in many situations that they otherwise couldn’t. The feature works regardless of whether you use autofocusing or manual focusing, and it works for both still photography and movie shooting.

However, when you use a tripod, the system may try to adjust for movement that isn’t actually occurring. Although this problem shouldn't be an issue with most Canon IS lenses, if you do see blurry images while using a tripod, try setting the Image Stabilizer (IS) switch (shown in Figure 1-4) to Off. You also can save battery power by turning off image stabilization when you use a tripod. If you use a monopod, leave image stabilization turned on so it can help compensate for any accidental movement of the monopod. If you shoot in the B (Bulb) mode, Canon recommends that you disable stabilization.

On non-Canon lenses, image stabilization may go by another name: anti-shake, vibration compensation, and so on. In some cases, the manufacturers recommend that you leave the system turned on or select a special setting when you use a tripod, so check the lens manual for information.

Whatever lens you use, image stabilization isn’t meant to eliminate the blur that can occur when your subject moves during the exposure. That problem is related to shutter speed, a topic you can explore in Chapter 7.

Getting acquainted with focusing

Your camera offers an excellent autofocusing system. With some subjects, however, autofocusing can be slow or impossible, which is why your camera also offers manual focusing. Chapter 8 fully explains automatic and manual focusing for viewfinder photography, and Chapter 4 explains how things work when you’re using the monitor to compose images (Live View mode) or are shooting movies. But here’s a primer to get you started:

❯❯ Choosing the focusing method: You set the focusing method via the AF/MF (autofocus/manual focus) switch on the lens. But be careful: If you’re in Live View or Movie mode, exit the live preview and return to viewfinder shooting before moving the lens switch from the AF to MF position. This step is needed to avoid damage that can occur if you switch to manual focusing while the continuous autofocusing system that's available for Movie and Live View modes engaged. (Chapter 4 explains this system and everything else about Live View and movie shooting.)

❯❯ Setting focus in MF mode: Just rotate the lens focusing ring. Figure 1-4 shows you where to find it on the 18–55mm kit lens.

❯❯ Setting focus in AF mode: Press the shutter button halfway to initiate autofocusing. After the scene comes into focus, press the button the rest of the way to take the picture. A couple pointers to remember:

● How the camera finds its focusing target and when it locks focus depend on autofocus settings that we detail in Chapters 4 and 8.

● If you’re using the 18–55mm kit lens (or any STM lens from Canon), turning the focus ring when in autofocus mode has no effect on the lens – it turns but does not focus and will never hit a physical stop. Both the 18–55mm and 18–135mm USM lens offer full-time manual focus when using one-shot AF. Simply press and hold the shutter button halfway, and then turn the focusing ring.

❯❯ Waking up a sleeping lens: With both kit lenses (as well as some other STM lenses), the focusing motor doesn’t operate if the camera has gone to sleep because of the Auto Power Off feature, which we explain in the section “Setup Menu 2,” later in this chapter. The lens itself goes to sleep if you don't perform any lens operations for a while. Either way, manual focus adjustments aren't possible when the lens is in this state, and automatic focusing during zooming may be delayed. You can wake the camera and lens up by pressing the shutter button halfway.

Two final Focusing 101 tips:

❯❯ If you have trouble focusing, you may be too close to your subject; every lens has a minimum focusing distance.

❯❯ In order to properly asses focus, you need to adjust the viewfinder to accommodate your eyesight, as outlined next.