Tom Clark - Digital Photography Composition For Dummies

I recommend shooting with a very high ISO only when you

|j-" Are in a low-light situation and have already determined that you can't further open up your aperture or slow down your shutter speed v• Want an artistic look in which noise would work to your advantage

Figure 3–5 shows a cropped-in detail of an image I photographed with my camera's minimum ISO and its maximum ISO. I took the image on the left with an ISO rating of 50, and it appears smooth and without flaws. I took the image on the right with an ISO of 3200, and it contains a lot of noise.

A histogram is a graph that displays the brightness distribution in an image. You can use your camera's histogram to determine how your total scene is being exposed. When photographing a scene, you use the histogram to determine whether you need to increase or decrease your exposure. (Check out your owner's manual to find out how to use your camera's histogram.) Figure 3–6 shows what a properly exposed image may look like in the histogram.

50mm, / sac, f/5.6, 50 50mm, 1/60 sac, f/5.6, 3200

Figure 3–5:The appearance (and lack) of digital noise in an image.

Shadows Midtones Highlights

Figure 3–6:A histogram for a properly exposed image.

The far left of the histogram in the figure represents black without detail, and the far right of the graph represents white without detail. A full-scale exposure (one that contains a full range of tonalities) has tonalities that range from black to white with everything in between. A full-scale exposure is the ideal in most situations. Some exceptions exist, however. For example, consider a scene that's supposed to be light, such as a snowy scene. In this case, most of the information would be skewed to the right. The opposite is true for a particularly dark scene.

If your scene's tonality is weighted heavily toward the left and is bunched up specifically at the very edge of the histogram, your image is underexposed. If the scene's tonality is bunched up on the right side of the histogram, your image is overexposed.

In digital photography, detail in your highlights is vital. If you overexpose your image, the detail in your highlights is gone for good. You can't recover highlight information in postproduction if it wasn't there to begin with. So, the best way to expose a scene is to capture detail in the highlights and to brighten the shadow areas (if necessary) in postproduction. For more on postproduction editing, see Chapter 18.

Your digital camera has a built-in light meter that determines how much light is available in a scene and helps you properly expose your image. The meter reads light that's reflecting off an element in a scene, and determines (based on your chosen ISO) how the level of light affects your digital sensor. Your camera then tells you whether you're underexposed or overexposed. You can compensate accordingly by altering your aperture, shutter speed, or ISO. (Read more about aperture, shutter speed, and ISO in the earlier section "Taking a closer look at aperture, shutter speed, and ISO.") Check out your camera's manual to discover where to see its meter readings and how to change your exposure settings.

You often can choose from four different metering modes, which you can read about in your camera's owner's manual. Each mode is useful for different subjects. Here are the modes and their uses:

0 Evaluative metering: This mode detects the subject's position based on where you place your focal point. (For more on focal point, turn to Chapters 2 and 7.) It reads the value of light all around the subject and compares its brightness to the rest of the scene to determine a proper exposure. Evaluative metering usually is the standard or default mode, because it's suited for most subjects and situations.

0 Partial metering:This mode reads the light information that exists in the center area of your frame. So, you must make sure your subject is in the center when you take your exposure reading. After that you can adjust your composition to position your subject somewhere else in the frame. Partial metering is most effective when your background is much brighter than your subject. This situation happens in backlit situations — when your subject is in front of the setting sun, for example.

0 Spot metering:This mode meters a particular element or area, so if you want to set your exposure based on one specific element in your scene, it's the best mode to use. Black-and-white film photographers mostly used spot metering to determine the various intensities of light in a scene. It isn't as commonly used in digital photography, however.

0 Center-weighted average metering: This mode uses the center of your frame to get a meter reading, and then it creates an average reading for the rest of the scene. Center-weighted average metering is sort of a mix

between evaluative and partial metering. Warning: This method isn't the most accurate, so I recommend that you not focus too much attention on it.

Using your camera's meter is a good way to get a general start to exposing an image, but I suggest that you look at your histogram for any particular scene after taking an image. If the histogram is bunched toward the left, increase your exposure (regardless of what your meter reading says), and if it's bunched toward the right, decrease your exposure. (Check out the earlier section "Using a histogram to check exposure" for more on histograms.)

Digital SLRs provide you with different types of automatic modes to work with based on your priorities. The following three modes are the ones you need to know about:

Full automatic:With this mode, you don't have to think about any of your settings. You don't have control over your aperture, shutter speed, or ISO settings, so you're free to concentrate fully on your compositions and communications with your subjects. Results may vary when using this mode.

Tv shutter priority:This mode gives you control over your shutter speed but handles aperture settings for you. If you want a fast shutter speed to freeze motion or a slow shutter speed to capture motion blur in a waterfall or a scene with cars driving down the street, this mode allows your camera's meter to determine your aperture settings. This mode comes in handy when shooting fast-paced sporting events. (Read more about photographing moving subjects in Chapter 16.)

Av aperture priority:This mode enables you to select your aperture, but it chooses the appropriate shutter speed for you. You'll find Av aperture priority mode handy when you desire a specific depth of field but aren't concerned with the speed of your shutter. You'll most likely use this mode on still subjects and when you have a well-lit scene or when your camera is on a tripod.

Check your owner's manual to find out more about the modes your camera includes and how to set them.

I recommend that you get into the habit of shooting manually. It's a lot like driving: A person who can drive a manual transmission can always drive an automatic in a jam, but a person who only drives automatic usually can't drive a stick if they ever have to. In other words, you want to be comfortable with your camera and its settings at all times just in case.

I sometimes switch my camera to automatic shooting modes based on convenience or necessity. One of those situations is when I'm shooting an event or wedding in conditions where the light intensity keeps changing. Rather than manually switching my settings back and forth, I let the camera do the work for me. I also use an automatic mode if I'm shooting in extremely low light and relying on an on-camera flash to light my scenes. Shooting in auto allows the camera and flash to work together in creating the most appropriate exposures based on the situation at hand.