Professional Information Technology-Programming Book part 7 ppt

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Professional Information Technology-Programming Book part 7 ppt

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2.5. Light Metering Tricks There are all sorts of ways to measure exposure. You can use one of your camera's metering modes in P shooting mode or (better yet) bracket a sequence of shots in half stop increments. You can look at the actual photo on your preview monitor after you shoot the test. Most cameras will also show you the exposure if you tell them to "show info." So, just pick the shot in your sequence that has the best exposure, get the info, switch to M mode, and set the exposure accordingly. Or you can shoot a gray card in spot metering mode. This ensures that you're only metering the image's midtones, so you should get the best compromise in exposure for all the prevailing levels of brightness. Your camera's color balance is calibrated at the same time, so you can set the white balance for all these exposures with one of the White Balance droppers that are available in both Photoshop and Camera Raw. In Photoshop Elements 4, you can only use an eyedropper to set white balance by choosing a Levels Adjustment Layer from the Layers palette. If the result is too much or too little brightness, you'll have to correct it by adjusting the midtone slider in the RGB channel (see Chapter 5). 2.5.1. Types and Uses for External Meters Although you can preview a shot and adjust your exposure according to the exposure information for that shot, there are times when an external meter can save time. That's because you can read for proper exposure before you start taking pictures. Also, most meters read exposure in such a way that you see a variety of aperture and shutter speed combinations that allow the transmission of equal amounts of light to be recorded by your sensor. That way, you don't have to do calculations each time you switch to manual mode but want to use a different shutter speed and aperture combination (see Table 2-1). Table 2-1. A chart of equivalent f-stop and shutter speeds at ISO 100 in average daylight. For each doubling of ISO speed, decrease the f-stop by raising it to the next highest number in the chart. Most digital cameras allow you to adjust both shutter and f-stop in half-stop increments. 1/8 sec 1/15 1/30 1/60 1/125 1/250 1/500 f-16 f-11 f-8 f-5.6 f-4.0 f-2.8 f-2 There are two types of meters that might come in handy: Incident and Spot. Incident light meters These meters are held in the area that is the center of interest and are pointed toward the camera. You set the ISO on the meter that will be the same ISO for your camera. You then press a button and the range of alternative exposures in Table 2-1 suddenly appears. Gossen makes an incident light meter that can measure either available light or strobe. You can see an incident light meter in Figure 2-9. Figure 2-9. An incident light meter being held as it is used to measure exposure. Spot meters Spot meters that aren't built-in generally look a bit like miniature telescopes and can be used to measure a small portion of the subject, even if it's too far away to get close to. If you frequently use long telephoto lenses, you might want to consider an external spot meter. However, if you shoot with a camera back or a DSLR, your built-in meter is measuring an area that is always within the angle of view for that particular lens. So there's far less need for a spot meter. Table 2-2 shows the ISO ranges of several popular DSLR camera models. Table 2-2. A chart showing the actual ISO ranges of several DSLR cameras. Canon 350D 100 200 400 800 1600 Canon 20D 100 200 400 800 1600 3200 option Canon 5D 50 option 100 200 400 800 1600 3200 option Canon 1DS Mk II 50 option 100 200 400 800 1600 3200 option Nikon D2X 100 200 400 800 1600 option 3200 option Nikon D200 100 200 400 800 1600 3200 option Nikon D70 Auto 200 400 800 1600 Nikon D50 Auto 200 400 800 1600 Olympus E-500 Auto 100 200 400 800 option 1600 option Olympus Auto 100 200 400 800 option 1600 option Pentax DL Auto 200 400 800 option 1600 3200 Pentax DS2 200 400 800 option 1600 3200 Fuji S3 Pro 100 200 400 800 1600 Minolta 7D Auto 100 200 400 800 1600 3200 Minolta 5D Auto 100 200 400 800 1600 3200 Contax 100 200 400 800 1600 2.6. Tricks for Steady Shooting Unintentionally blurry pictures are almost always the first to the trash. Most of the time, it has nothing to do with the movement of the subject, but with the fact that you haven't been careful enough to keep the camera steady. So it pays to practice avoiding blurry shots that happen because a camera is too unsteady for the shutter speed called for by the conditions of lighting and subject motion. Of course, there are ways to minimize or even ensure that the camera won't move when the shutter fires. 2.6.1. Antishake Mechanisms There's at least one DSLR manufacturer, Sony (Alpha 100 DSLR), that has an antishake mechanism built into its sensor. It's a feature I wish all DSLR makers would offer, especially those that have higher-resolution (8+ MP) sensors. The advantage is that the antishake mechanism works for up to a three-f-stop diff erence in exposure. So a nightclub shot that had to be taken at ISO 400 at 1/80th of a second can now be taken at 1/20th of a second. If you shoot a lot of news, parties, and events, it's worth having one of these camerasyou'll hardly ever have to shoot with flash. Heck, even when you do shoot with flash, you could use a slow enough shutter speed to get a lot more detail in the background that isn't motion blurred. If you have a DSLR that doesn't have built-in anti-shake (aka image stabilization)particularly a higher-resolution, lower-noise oneall is not lost. Most lens vendors make antishake lenses. The bad news is that you will pay significantly more for the lens. Furthermore, you have to buy one in every focal length you need the feature for. Heaven forbid you have to shoot both wildlife and weddings. 2.6.2. Bracing and Breathing By far, the most common situation you will find yourself in is simply holding the camera in your hands while you grab a shot before the opportunity flits away. So you want to keep your shutter speed at around 100th of a second, just to ensure a reasonable chance of sharpness. Wide-angle shots are less likely to appear blurry than telephoto shots. Telephoto lenses much more than 150mm in effective length require either a rock-steady camera or some image stabilization mechanism in the camera. If you don't have a tripod, or the time to set one up, brace yourself by leaning against something solid. If you're near a flat surface like a table top or guard rail, brace your elbows on it. If you're not, press your elbows tight against your torso. Take a deep breath. Just before your lungs are filled and you have to let your breath out, squeeze the shutter button so smoothly that you're surprised when you hear the shutter (or mirror) click. You can also use your camera strap to make sure the camera is steady. Put your elbows inside the strap and then spread your arms so that there is tension between your body and the camera. Once you've done all the above, reduce the shutter speed to about one-fifth of a second and make a test shot of a motionless subject. Press the Preview button and then do what your camera requires to enlarge the preview image to 100 percent (or more). If the edges of the subject are sharp, you've either got it down or got lucky. Try this a few more times until you know you've got it down. Repeat this exercise every time you get a chance until you are so good at it that you can shoot at even slower shutter speeds. I have a friend is so good at it that she can hand-hold for a full second. Figure 2-10 shows a photographer practicing all of the above. Figure 2-10. A photographer taking all the steps to keeping the camera steady when there's no chance of setting up a tripod. 2.6.3. Tripods and Monopods Surely nobody who is reading this book doesn't know what a tripod is. Just in case you don't, though, it's a three-legged stand with variable length legs and a swiveling head that screws tightly to the bottom of your camera. The bigger and tougher the tripod, the steadier it's likely to be. However, the trick is to get one that's just big, steady, and precise enough to keep your camera motion-free. After all, if it's too heavy, you'll never take it with you. The tripod you need for a point- and-shoot could be about half the weight of the one you need for an entry-level DSLR, for example, as cameras grow in size and price. One big caution: don't use a tripod that doesn't stay adjusted while you're working. A funky tripod head or leg tightener just isn't worth having. Furthermore, they become looser and more useless over time. The more you tighten them up, the looser they get. Tripods are expensive, but look for one that is unusually steady for its lightweightness. If you see the words magnesium alloy or carbon fiber, you're probably in good shape. Figure 2-11 shows you a reasonably priced tripod. Figure 2-11. Popularly priced but sturdy tripod with a ball head. Let's face it; sometimes tripods are just too much of a pain to lug around. A monopod can do very nearly as good a job, as long as you brace it. A monopod is, essentially, one tripod leg with four, rather than three, sections so you can collapse it to about a couple of feet in length. For hikers, monopods can also double as walking sticks. NOTE It is much harder to keep the camera in exactly the same spot between shots when using a monopod. Therefore, they're rarely suitable for making multiple exposures for use in a panorama, stitched mosaic, or HDR image. (See Chapter 11 for more on HDR.) 2.6.4. Shoot, but Don't Touch One of the most common causes of unintentional camera shake is the act of punching the shutter release. The remedy? Squeezedon't push. You want to be so gentle with your depression of the shutter release that you are a bit surprised when you hear the shutter click. An even better solution is a device that makes it possible to fire the shutter without touching the camera at all. The devices used for touchless shutter release are even more valuable when the camera is just placed on a flat surface for bracing, rather than on a tripod or clamp. The best, cheapest, and most old-fashioned of all touch-free shutter releases is something called a cable release (see Figure 2-12). You can buy one for next to nothing, and it is always reliable. Figure 2-12. A cable release. Making a camera that has a cable release socket doesn't cost a single penny more, either. It's just that crafty camera makers have found a way to boost their profit margins by not drilling a threaded hole in the shutter release button. You then have to buy an electronic device known as a remote control. Really reliable remote controls are wired to the camera because they go off the instant you push the button. The more common type is infrared. The disadvantage here is that there has to be a clear line-of-sight between the remote control device and the infrared receptor on the front of the camera. Of course, if you're not careful, holding it in front of the camera can be difficult without including it in the picture. Once again, practice to the rescue. Before you have to use the remote, practice your holding position when you're shooting with it until you don't see anything in front of the lens that shouldn't be there. . External Meters Although you can preview a shot and adjust your exposure according to the exposure information for that shot, there are times when an external meter can save time. That's because. DSLR, your built-in meter is measuring an area that is always within the angle of view for that particular lens. So there's far less need for a spot meter. Table 2-2 shows the ISO ranges. 800 1600 option 3200 option Nikon D200 100 200 400 800 1600 3200 option Nikon D70 Auto 200 400 800 1600 Nikon D50 Auto 200 400 800 1600 Olympus E-500

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