Digital Photography

When you shoot in any autoexposure mode — full auto, scene modes such as Portrait or Landscape, or semi-automatic modes such as shutter-priority and aperture-priority autoexposure — the camera’s autoexposure brain determines what constitutes a good exposure and then adjusts the necessary exposure settings (f-stop, aperture, and ISO) accordingly. That’s all well and good, but what if you disagree with the exposure results? Easy: You can use a feature called EV Compensation to tell the camera to produce a picture that’s a little brighter or darker than what it originally delivered. (The EV in EV Compensation stands for exposure value.)

Using this control is easy. Here’s what you need to know:

• Look for a button or menu option that’s marked with a +/- sign (like this ) or the sign along with the letters EV.
• The available settings are presented either with a plus sign, such as EV +0.3, or a minus sign, such as EV -0.3.
• A setting of EV 0.0 indicates that no exposure adjustment will be made.
• If you want your next shot to be brighter, dial in a positive EV number; for a darker picture, select a negative EV number. The balloon photo here, from my book Nikon D60 For Dummies, offers just one example. In the original shot, the sky is perfectly exposed but the balloon is too dark. Raising the EV value to +1.0 produced a better result.
• EV settings are typically available in either 1/2-step increments, such as +0.5, +1.0, +1.5, and so on, or in 1/3-steps, such as +0.3, +0.7, and +1.0. The range of settings you get, and therefore the level of exposure adjustment you can make, varies from camera to camera.
• How the camera arrives at the brighter or darker image depends on your exposure mode. In shutter-priority mode, for example, the camera will stick with the shutter speed you selected and adjust either ISO or f-stop to produce the darker or brighter exposure. In Full Auto mode, the camera may adjust shutter speed, f-stop, ISO, or all three as needed.

Only one word of caution: Depending on your camera and the exposure mode, the EV setting may or may not automatically be reset to a neutral EV 0.0 when you turn off the camera or switch exposure modes. If your camera doesn’t reset the option for you, it’s a good idea to get into the practice of resetting to EV 0.0 yourself after you’ve gotten the shot you’re after. Otherwise, you may forget that exposure compensation is in force.

Remember when you used to buy film, and it came in different “speeds” — ISO 200, 400, 800, and so on? Well, those numbers indicate the film’s sensitivity to light; the rating system was devised by the International Standards Organization, thus the ISO abbreviation. The higher the number, the “faster” the film, meaning less light is needed to expose the picture. So a high ISO film lets you use a smaller aperture (higher f-stop setting) or faster shutter speed than if you use a low ISO film. (If that last sentence sounded like gibberish, check out my previous posts, which provide the fundamentals of exposure.)

On a digital camera, the ISO setting determines the light sensitivity of the image sensor. And just as with film, using a higher ISO setting allows you to capture an image with less light. Most cameras enable you to choose from a range of ISO settings, typically from about 200 to 1600, although some newer, higher-end cameras offer much wider ISO ranges, starting as low as ISO 50 and going as high as ISO 6400 or even greater.

Unfortunately, increasing ISO brings a negative side effect: Your picture can take on a grainy or speckled appearance. The example here (a portion of a flower petal) gives you a close-up look. This example shows the digital version of the problem, but you get a similar result with film. In the digital world, the defect is called noise; in the film arena, it’s known as grain.

If you’re an experienced film photographer, you probably know that different types of film produce different levels of grain at a given ISO. Similarly, digital cameras also vary in their noise performance. You may not see any noise at ISOs up to 1600 on some cameras, while others produce visible noise at ISOs as low as 800. It’s important to run a test on your camera so you know just where the level of noise becomes objectionable. Shoot the same subject at each of your camera’s ISO settings and inspect the results. Then, when you’re shooting in dim lighting, you can decide whether you’re better off raising the ISO to get the shot or using a slower shutter speed or lower f-stop setting. Remember that slow shutter speeds can result in motion blur, and your f-stop setting affects depth of field, so you have to balance all three concerns when choosing your exposure approach.

Also check your manual to find out what exposure modes allow you to control the ISO setting. On some cameras, you get no say-so when you shoot in the Full Auto mode or the automatic scene modes (Portrait, Landscape, Sports, and so on). The camera automatically adjusts ISO as needed, always favoring a bright-enough exposure over any noise considerations, and you have to use an advanced exposure mode, such as aperture-priority or shutter-priority mode, to regain the ISO reins. But other cameras let you specify ISO in any exposure mode.

Offering the best of both worlds, some cameras give you an Auto ISO setting but enable you to set limits on the automatic adjustment. Here’s how this feature works: You specify your preferred ISO, but you give the camera permission to adjust ISO if it can’t exposure the picture at your chosen f-stop and shutter speed. In most cases, you also can tell the camera not to go above a certain ISO setting and to intervene only if the shutter speed drops below a certain number.

One final ISO comment: Many cameras offer a built-in noise-removal filters. These filters attempt to soften the appearance of noise by applying a slight blur to your photo as it’s being processed and written to your memory card. They may, in fact, help with noise, but they create new problems: First, you lose a little image sharpness due to the blur, and the camera needs more time to process your photo, hampering your ability to fire off a rapid series of shots. So I leave these in-camera filters off and then use my photo editor’s blur tools to try to soften noise if necessary. Doing the repair in a photo editor lets you limit the blur to the worst parts of the image rather than losing sharpness throughout the whole photo.

Does your camera offer shutter-priority autoexposure mode? Look on your exposure mode dial — it should be marked with the letters S or Tv. If you do have access to this mode, you’ve got a great tool for shooting scenes that contain movement, whether it’s your youngster lobbing tennis balls, a ferris wheel at the state fair, or even a flower blowing in the breeze.

In case you’re new to the concept of shutter speed, here’s a quick lesson: The shutter is a barrier inside the camera that prevents light from striking the image sensor (the part that turns light into a photograph). When you press the shutter button, the shutter opens briefly to let light through to the sensor. Shutter speed, measured in seconds, refers to how long the shutter remains open. In other words, shutter speed determines the exposure time – thus the abbreviation Tv (for time value) that’s used on some cameras to indicate shutter-priority autoexposure mode.

The shutter speed affects more than just how bright your photo is, though. It also determines whether any movement of your subject or the camera creates blur. Here’s the short story:

• Fast shutter speeds “freeze” motion; slow speeds blur it. Exactly how fast you need to go to freeze motion depends on the speed of your subject — the faster it’s moving, the higher the shutter speed you need. For example, check out the rose photo here, from my soon-to-be published tome, Nikon D90 For Dummies. Most people probably wouldn’t think “action shot” when photographing a flower, but if the wind is blowing, you need to see it as such. On the day I took this picture, a shutter speed of 1/40 second wasn’t fast enough to compensate for the motion of the flower, as you can see in the left example. I increased the shutter speed to 1/80 second to catch the blur-free version on the right. But if you were trying to shoot, say, an inline hockey player or a bird in flight, 1/80 second wouldn’t be nearly fast enough. So some experimentation is needed (although 1/1000 second should be fast enough for all but the speediest subjects).
• You can use very slow shutter speeds to your creative advantage, too. Experiment with using a very slow shutter speed — say, 1 second or more — to purposely blur motion for special effect. That’s how photographers produce those misty waterfall shots and ”trails of car lights” images you see in nighttime city scenes.
• But be careful about camera shake when using a slow shutter! Even the smallest movement of the camera during the exposure will blur the entire picture, not just moving objects. And the slower the shutter speed, the longer you need to keep the camera still. For most people, it’s tough to handhold a camera successfully at speeds much below 1/50 second, although the anti-shake features found on most new cameras do enable steady shooters to drop a little below that threshold. When in doubt, use a tripod or otherwise stabilize the camera to avoid the problem.

Now that you understand the relationship of shutter speed to blur, you can be more creative with your “moving pictures,” deciding whether you want to stop action or blur it. And with shutter-priority autoexposure, you can concentrate on shutter speed and rely on the camera to make the other necessary exposure calculations. You dial in the shutter speed you want, and the camera automatically takes care of the other two critical exposure settings, f-stop and ISO. (Check out the last several posts for details on the whole business of calculating exposure.)

Note just a few final details about shutter-priority mode:

• As you adjust the shutter speed, the camera has to adjust f-stop, ISO, or both to maintain the proper exposure. Remember that the f-stop setting  affects depth of field, or the range of sharp focus, while high ISO settings can produce the speckled defect known as noise. So after you select the shutter speed, verify that the f-stop or ISO the camera selected in turn won’t be a problem. For my rose photo, I was already at the lowest possible f-stop setting (f/6.3) for the lens I was using (meaning the aperture was wide open), so in order to use a faster shutter, I had no choice but to raise the ISO to 400. Fortunately, that’s well below the noise threshold on most cameras.
• The range of shutter speeds available to you depends on the camera; check your manual for specifics.
• With most cameras, using flash limits you to a top shutter speed in the 1/200 - 1/250 second range. However, if you can attach an external flash head to your camera, you may have more flexibility — it all depends on the camera and the flash.

Over the past week or so, I’ve been opining about how exploring advanced exposure modes can help you take more creative control over your photos. Today I want to introduce you to one of the two common semi-automatic modes, aperture-priority AE (autoexposure.) Represented on camera mode dials or menus by the letter A or Av (for aperture value), it offers you an easy way to manipulate depth-of-field, or the zone of sharp focus in a photograph.

Just a quick recap of aperture basics: The aperture is an adjustable hole in a diaphragm that sits behind the lens in your camera. Through the camera’s aperture setting, you can change the size of that hole, allowing more or less light into the camera. The size of the aperture is stated in f-numbers or, more commonly, f-stops, and is written as f/2, f/5.3, and so on.  The lower the f-stop number, the larger the aperture, and the more light that’s allowed to into the camera.

But as I mentioned, changing the aperture size also impacts depth of field. A low f-stop produces a short depth of field, so your subject appears sharply focused but distant objects are blurry. A higher f-stop increases depth of field, so those distant objects appear more sharply focused. The photos here, from Digital Photography For Dummies, 6th Edition, offer an example. I took the first picture using an f-stop of f/3.4, and the second at f/11. Notice that the background is less sharply focused in the f/3.4 example than in the f/11 example.

Of course, as you allow more or less light into the camera, you have to adjust one of the two other exposure controls, shutter speed or ISO, to maintain the same exposure. And that’s the cool thing about aperture-priority autoexposure: The camera takes care of the needed shutter speed or ISO adjustment for you. .) All you do is decide how much depth of field you want and then dial in your preferred f-stop setting. (Whether the camera manipulates just shutter speed, ISO, or both depends on the camera, so check your manual.)

Do note a couple of fine points about aperture-priority AE:

• The range of aperture settings you can choose depends on your camera and lens. (Again, your manual will spell out the details.)
• In dim lighting, check to see what shutter speed the camera has selected after you set the f-stop. Be careful that the shutter speed doesn’t drop so low that movement of your subject or camera shake will blur the photo (anything below about 1/50 second takes you into the danger zone). For still subjects, use a tripod to avoid the problem. For moving subjects, you’ll either have to raise ISO or compromise on f-stop to get the shutter speed up.
• If the camera can’t select a shutter speed or ISO that will properly exposure your photo at your chosen f-stop, it should alert you in some way — blinking values in the viewfinder or monitor, for example. You can then choose to either go forward and take the picture or adjust the f-stop.
• Changing the aperture isn’t the only way to manipulate depth of field. You can also zoom in or move closer to your subject to reduce depth of field; zoom out or back away to increase it.

Okay, enough verbiage. Time to go get your camera and do some experimenting. Once you get a feel for aperture-priority mode, it’ll become your go-to mode for most still subjects, whether it’s a portrait, still life, product shot, landscape – you name it. Shoot each scene at several different aperture settings so that you can get a clearer idea of just how much playing with f-stops can affect your pictures.

Over the last week or so, I’ve been nagging you to take your camera out of Full Auto mode so that you can control aperture (f-stop), shutter speed, and ISO to suit your creative vision. But precisely how much control you have over those three major exposure settings depends on your camera, so dig yours out and let’s do a little inventory of your options.

Start by locating your camera’s exposure mode dial or switch. On a digital SLR, it usually looks something like the picture here, which shows a dial from a Canon Digital Rebel model. Compact cameras often sport a smaller version of the same dial, although in some cases you may have to dig into the camera’s menus to uncover all your options.

Here’s a list of the most common modes:

• Full Auto: Usually represented by the word Auto, a rectangle (as here) or little camera icon, this one leaves all exposure settings up to the camera. 
• Automatic Scene modes: These are the modes represented by the little pictographs. They’re designed to automatically select aperture and shutter speeds that work best for different types of shots. For example, in Portrait mode, the camera chooses a low f-stop, which reduces depth of field so that the background will be in soft focus; in Landscape mode, the camera dials in a high f-stop to keep both background and foreground sharp. And Sports mode gives you a fast shutter speed to help you capture moving subjects. The range of scene modes varies widely from camera to camera, so you’ll need to check your manual to find out what options you have. The names given to the scene-mode feature vary, too; for example, Nikon uses the term ”Digital Vari-Program modes”; Canon goes with ”Image Zone” modes.
• Programmed auto (P): In this mode, the camera selects the aperture and shutter speed it thinks will work best, just as in full auto mode. But typically, you can then choose from a few other combinations that will deliver the same exposure, so you get some — but not much — control over f-stop and shutter speed. Some manufacturers refer to this mode as flexible programmed auto.
• Shutter-priority autoexposure (S or Tv): In this mode, you set the shutter speed, and the camera selects the correct aperture setting for you. (The Tv stands for time value; remember, the shutter speed controls the exposure time.) It’s great when you’re shooting action and shutter speed is critical — your priority, if you will.
• Aperture-priority autoexposure (A or Av): In this mode, you select the f-stop, and the camera then chooses the right shutter speed to properly expose the picture. (The Av stands for aperture value.) This mode is perfect for shooting portraits, landscapes, and other still subjects because it enables you to manipulate depth of field through the f-stop setting.
• Auto Depth of Field (A-DEP): This one’s found on some Canon cameras. It analyzes the scene and then tries to select an aperture setting that will produce the depth of field needed to keep all major objects in sharp focus. However, a good exposure is favored over f-stop, so in some lighting conditions, the camera may not select a setting that achieves the depth-of-field goal.
• Manual (M): In manual mode, you dial in both aperture and shutter speed. The camera does offer some assistance, however, by presenting an exposure meter or some other guide to let you know whether it thinks your exposure settings are off the mark.

You may have noticed that my descriptions don’t say anything about ISO. That’s because how much you can control ISO in each mode depends on the camera. So again — regretfully — I must refer you to your manual for that bit of detail.

The other important thing to know is that on most cameras, the Auto and Scene modes usually limit your photographic choices beyond exposure. Usually, you can’t tweak color or control flash, for example. And  as with A-DEP mode, whether the camera can choose an appropriate f-stop or shutter speed for your subject depends on the lighting conditions. For example, in a dimly lit gym, the camera probably won’t be able to select a shutter speed fast enough to stop action even in Sports mode.

As for Programmed Auto and A-Dep, well, their main benefit is that they won’t allow you to choose settings that under- or overexpose your picture. But because you can always check exposure in your monitor, I suggest that you bypass those two modes in favor of aperture-priority and shutter-priority autoexposure, if your camera offers those modes. Then you can dial in a specific f-stop (with aperture-priority mode) or shutter speed (with shutter-priority mode), depending on your creative point of view.

Manual mode? Well, when you get proficient at manipulating exposure, you’ll probably want to shift into that mode because it’s the only way you can control both f-stop and shutter speed. But when you’re just starting to understand exposure, the “priority” modes offer the best combination of control and autoexposure support. In upcoming posts, I’ll tell you a bit more about using these two modes to your best advantage.

My previous post, which introduces you to the “Big 3″ of digital camera exposure controls — aperture, shutter speed, and ISO – explains that you can achieve the same image brightness by using many different combinations of these settings. (If you haven’t read that post, scroll to check it out now, or the rest of this probably won’t make much sense.) I also alluded to the fact that each of these settings impacts your photograph in ways that go beyond mere image brightness.

Understanding these side effects, in my opinion, is one of the most important things you can do if you want to shift from mere picture-taker to photographer. Why? Because through your choice of aperture setting (f-stop), shutter speed, and ISO, you can put your creative stamp on a scene and control picture quality in the following ways:

• The aperture setting (f-stop) affects depth of field. A low f-stop number produces a shallow depth of field. That means that your subject is in sharp focus, but objects at a distance appear blurry. A high f-stop number enlarges the zone of sharp focus so both your subject and distant objects appear sharp.
• Shutter speed determines whether moving objects appear blurry. A fast shutter speed “freezes” a moving object; at a slow shutter speed, the object appears blurry. A slow shutter speed also causes all-over image blur if you move the camera during the exposure.
• ISO affects image noise. Noise is a defect that makes your image appear speckled. As you raise the ISO, you increases the chances of noise. (The defect is similar to what you see when you shoot film pictures using high ISO film.) For this reason, you should always use the lowest ISO setting possible given the current lighting conditions.

The two pictures here, taken from my book Canon EOS Digital Rebel XSi/450D For Dummies, offer one example of how you might choose different aperture and shutter speed settings depending on your creative goal. I took the left picture using an aperture of f/13, a shutter speed of 1/25 second, and ISO 200. For the right picture, I again used ISO 200 but reduced the f-stop setting to f/5.6. That in turn reduced depth of field, so the background building is less sharply focused than in the f/13 shot. Of course, lowering the f-stop opens the aperture, letting more light into the camera, so in order to maintain the same exposure, I had to either lower the ISO (making the camera less sensitive to light) or use a faster shutter speed, shortening the exposure time. For this example, I choose the latter, raising the shutter speed to 1/125 second. This choice, too, affected my picture because the scene contains motion — the spray coming from the fountain. Notice that at a shutter speed of 1/25 second, the water appears blurrier than in the 1/125 second shot. (Using a very slow shutter speed is how nature photographers produce those “misty waterfall” images.)

Now that you have an idea of the possibilities, it’s time to find out how much your camera enables you to control aperture, shutter speed, and ISO. The answer depends on how many exposure modes your camera offers. Tune in tomorrow to get a rundown of the most common exposure modes and the level of control each offers. Even if you have a pretty basic point-and-shoot compact camera, you may have more flexibility than you know.

In yesterday’s musings, I urged you to take the leap beyond shooting in fully automatic exposure mode and promised to give you the basic exposure info that will help you do just that. So here goes . . .

First, you need to know that a camera produces a photo by focusing light through a lens onto a light-sensitive recording medium.  On a digital camera, that medium is the image sensor, which is essentially just a bunch of light-reactive computer chips. The exact design of this optical system varies depending on the type of camera, but the simple illustration here, taken from Digital Photography For Dummies, 6th Edition, gives you an idea of the traditional setup. 

Notice that between the lens and the sensor are two mechanisms, the aperture and shutter.  These two components work together to determine how much light reaches the sensor:

• Aperture: The aperture is a hole in a adjustable diaphragm behind the lens. By changing the size of the aperture, you can let more or less light into the camera. Aperture size is stated in terms of f-numbers, or f-stops in common lingo, as in f/2, f/5.4, and so on. The smaller the number, the larger the aperture, and the more light enters the camera. The range of aperture settings available to you depends on your camera lens.
• Shutter: You can think of the shutter as sort of like blinds on a window. Normally, the shutter is closed, preventing light from striking the sensor, just like closed window blinds prevent the sun from waking you up at some ungodly hour. When you press the shutter button, the shutter opens briefly, as shown in the illustration, to allow light that comes through the aperture to strike the image sensor.  Shutter speed refers to the length of time the shutter remains open and is stated in seconds or fractions of a second — 1 second, 1/60 second, and so on. Again, the range of shutter speeds you can use depends on your camera.

A third exposure control, called ISO, determines how much the camera’s image sensor reacts to light. ISO stands for International Standards Organization, which is the international group of poohbahs that developed a universal system of numbers for rating the sensitivity of photographic mediums. The higher the number, the more the medium reacts to light. On most digital cameras, you can choose from several different ISO settings. (Note that we’re not talking about a mechanical structure here, but a computerized function that boosts the reactivity of the image sensor.)

Summing up, you have a three-part equation that determines the brightness of your image:

• Aperture (f-stop) setting = amount of light
• Shutter speed = duration of light
• ISO setting = the sensitivity of the sensor to light

In the days before autoexposure cameras, photographers had to measure the light (using a light meter) and then determine the proper aperture and shutter speed based on the ISO of the film being used. Today, of course, you can let the camera take care of all the light metering and exposure decisions for you. So, you’re wondering, what exactly do you gain by even worrying about all this stuff?

Well, it turns out that each of these settings also affects your photo in ways that go beyond the mere brightness of the photo. In the next couple of posts, I’ll talk about those side effects and how you can use them to your creative advantage.

I had a conversation the other day with someone who wasn’t satisfied with the pictures he was taking and wanted to know whether buying a better camera would help. I asked what camera he was currently using, and discovered that he already owned a top-notch digital SLR model - sure, it was a year old, but it still was a great camera and certainly capable of producing excellent images. Digging a little deeper, I found out that he had never taken his camera out of its fully automatic, “point and shoot” mode. So my answer to his question was easy: A new camera wasn’t going to make him any happier. What would make a difference was spending a little time learning how to use his camera’s other exposure modes.

Don’t get me wrong - you can shoot some great photos in Auto mode. But you really can’t put your creative stamp on a scene until you wrest at least a little control from the camera. For example, with most cameras, you can’t use flash in bright sunlight in Auto mode, even though a little pop of flash can really improve many outdoor photos, as illustrated by the two examples here. The left image is the flash-free version; I took the second using my camera’s built-in flash. You also can’t fully manipulate depth of field, or the distance over which objects remain sharply focused in a scene. Additionally, many cameras don’t let you access options that affect color, such as the White Balance setting, in Auto mode.

So this year, resolve to move beyond Auto mode, if your camera offers that option. Where to start? Well, the first step is to get a grip on the three factors that determine exposure: Aperture (f-stop), shutter speed, and ISO. Each of those controls affect your picture in ways that go beyond mere image brightness, and learning how to use those side effects to your advantage will make a huge difference in your ability to capture a subject the way you envision it in your mind’s eye.

 In the next few postings, I’ll provide the specifics you need to master all three settings and introduce you to two semi-automatic exposure modes that offer an easy way to step your photography up a notch.