Get the Most From Your Digital SLR

Transcription

1 Get the Most From Your Digital SLR Lesson Three: Metering, Histograms and ISO Table of Contents Introduction... 1 Definitions... 2 Metering Modes... 2 Area (or Evaluative) Metering... 2 Center-Weighted Metering... 3 Spot Metering... 3 Histograms... 4 A Basic Histogram... 5 Histogram vs. Light Meter... 5 Histograms and Dynamic Range... 8 Exposure Bracketing... 9 ISO ISO Example Moderate Light, Fast Action Increasing Depth of Field With ISO The Catch The ISO Chart Adjusting Color With White Balance White Balance Color Enhancement Mixed Light Sources Conclusion Exercises Introduction Here we go - ready for lesson three? I hope that by now you've had plenty of time to play around with you camera's aperture and shutter speed, and that you have a much better understanding about how the two of them interact to create a balanced exposure. This knowledge foundation is critical. It's critical because a lot of the concepts in this lesson are going to build on the principles of exposure. If the previous lesson still doesn't make a lot of sense, this one will confuse even further. Part of the problem is that I'm about to dig into some of the lower-level features that your digital SLR has to offer, and I don't want you to get too far along if the high-level features still aren't making any sense. If you've worked through lesson one and two several times and are still perplexed, please feel free to contact me. I'll be happy to help you clarify any feature or technique that you're stuck on.

2 Definitions The bad news: we've got a lot of definitions to cover in this lesson. The good news: these definitions are shorter and the concepts should click pretty fast if you really understand aperture and shutter speed. The better news: some of the terms and technique in this lesson will take your digital SLR knowledge from casual to semi-pro. Once you're done, you'll really be able to impress all of your point-and-shoot friends with your in-depth knowledge of digital SLR cameras. Metering Modes In lesson two, I introduced you to the concept of dynamic range. You learned that your camera cannot always capture what your eyes can see, especially if there's a lot of contrast in the scene you're photographing. Faced with extreme contrast, the camera either exposes for shadows or highlights, but it can't capture both. Here's the kicker: even if you're in manual mode, and set the meter to a balanced exposure (the zero point) your photo STILL might not turn out the way you want it to. The problem here is the metering mode that your camera is using. There are three main types of metering modes: 1. Area (or Evaluative) 2. Center-weighted 3. Spot Let's talk about each one of these in turn. Area (or Evaluative) Metering The marketing departments of the various camera manufacturers just love to tout the efficiency and range of their area metering systems. While it's true that some area meters are better than others, it's important for you to understand this: regardless of how "smart" the metering sytem is, it can and will make bad judgement calls when faced with challenging light. Here's what all area meters do: they evaluate ALL of the light that's entering the lens to make a judgement about what exposure settings to use (the orange tinted area in the image represents what the area meter is using to judge exposure).

3 Imagine that you're taking a photo that is split 50/50 between light and dark. Half of the scene is in the shade and the other half is in bright sunlight. In this instance, the camera is trying to get an exposure reading based on BOTH the shadow and the light. When your meter is at the zero point, that will really just be a middle ground in between the highlights and the shadows (because the camera can't capture both due to limited dynamic range). Area metering is the most common metering setting, and it works best for landscapes, where you're trying to ensure that everything you see in the viewfinder comes out correctly exposed in your final image. Center-Weighted Metering Sometimes you don't want to be metering everything that you can see in the viewfinder. Think about portraits: in this case, your subject is pretty much in the center of the image. If you have your camera set to area metering when you're taking a portrait a bright highlight or dark shadow in the background can throw off the exposure of your primary subject. This is especially true if your subject is standing in shade with bright sunlight behind her. When area metering is activated, it sees all of that bright sunlight and tries to tone down the exposure to compensate. End result? Your primary subject winds up under exposed. The way to balance this is to set your camera to center-weighted metering. In this case, the camera only meters an area that is directly around the center focus point in your camera's viewfinder. A center-weighted meter will ignore the light around the edges of the image and won't take it into account when it's trying to judge exposure. When you have your metering set to center-weighted and your primary subject is in the center of the viewfinder, you can rest assured that the exposure reading is accurate (when the meter reads zero, your subject will be correctly exposed). This type of metering works well for portraits, and any time your are taking a photo of a subject in shade that is surrounded by bright sunlight. Spot Metering Spot metering is just center-weighted metering taken a step further. When you activate the spot meter, the camera only judges exposure settings based on the light that is

4 directly in the center of the viewfinder (right around your center focus point). Spot metering is used to gain very precise exposure readings, and is used under special types of lighting conditions. Imagine that you are taking a portrait with a telephoto lens. You want to ensure that your subject's face is correctly exposed, but you're less concerned about how the rest of the image turns out (it's fine if it's over or under exposed). Since you're standing so far away from your subject, you need to precisely meter her face. Activate your spot meter, point the camera at your subject's face, and adjust aperture and shutter speed so that the meter reads zero. Spot meters also have another more advanced use. In lesson two we went over dynamic range, and I showed you an example of a beach at sunset. In the case of that example, the camera could either capture detail in the highlights OR the shadows, but not both. But let's say that you want complete control over how your camera exposes a scene with a lot of contrast. In this case, switch of the area metering and set your camera to spot metering mode. If you point your camera at the highlights, the meter reading will point to zero when the highlights are correctly exposed (but shadows will be VERY dark). If you point your camera at the shadows, those will be correctly exposed but highlights will be pure white. In this fashion, you can get a correct exposure reading based on what's most important to you. Imagine that your subject is a deer standing at the edge of a glade. The deer is in shadow, but the glade is in bright sunlight. Since the most important part of this image is the deer, use your spot meter on it to ensure a proper exposure, and let the sunlight in the glade expose however it wants to. Histograms I spent a large portion of lesson two telling you that your camrea's meter reading is not always accurate, and that there are many times when you need to compensate by intentionally over or under exposing. Conditions that typically trip up an SLR meter include snow, fog, sand, shade and any scene with extreme contrast variation. There's one approach to getting correct exposures every time: memorize all the camera adjustments that you have to make depending upon your subject and lighting conditions. This is not only slow and laborious, it also won't be 100% accurate over time. The good news is that there's a much better and faster way to tell when your images are correctly exposed. All you have to do is check your histogram.

5 Here's the 10-second definition: A histogram is a graphic display of the light and dark elements in your photo. OK, but what makes a histogram so useful? Here it is: unlike your camera's light meter, a histogram ALWAYS shows you if your photo is under or over exposed. Let's take a look at how this works. A Basic Histogram Here's a photo and its histogram: Every digital photo that you take is a combination of millions of individual dots of color called pixels (a 10 megapixel photo includes 10 million pixels). The histogram chart shows you two things: 1. The scale along the bottom of the display goes from dark pixels (on the left) to light pixels (on the right) 2. Mid-tones (neither light nor dark) fall in the middle of the scale 3. The vertical axis shows you the proportion of light, dark and mid-tone pixels in your photo The higher the peak of the histogram, the more pixels you have within a certain brightness level. For example, if the peak of your histogram is to the left, this tells you that your photo is predominantly dark. If the peak is over to the right, the tones in your photo are mostly light. If your histogram looks like a bell curve (where the peak is in the middle and it tapers off at both ends) then your photo includes a lot of mid-tones and probably doesn't have a lot of contrast. Histogram vs. Light Meter We now know two things: 1. Light meters can get confused sometimes and will "lie" about the correct exposure setting (they don't mean to, really)

6 2. Histograms never lie about how many light and dark pixels you've captured in your photo Since the histogram is not as easily confused as the light meter, we can use it to challenge the light meter's assumptions about the amount of available light. This will be easiest for you to understand if we just walk through an example. For each photo, I'll explain why the light meter thinks the images is properly exposed (when it isn't) and what compensation you'll have to make (using the histogram) to get the exposure right. These photos were taken in Aperture Priority mode, with a fixed aperture of f/5. Shutter Speed: 1/160 This first image is under exposed, with the meter set squarely to zero. What's the problem? It's an overcast day - one of the most common times when a digital SLR camera will under expose a photo, even with the meter set to zero. You can see that the peak of the histogram is over to the left side - meaning that there are far more dark pixels in the photo than light ones. In order to get a better exposure, I'm going to have to intentionally over expose using exposure compensation. I'll start by setting my compensation (still in Aperture Priority mode) to +1/3. Shutter Speed: 1/125

7 You can see that the histogram has shifted slightly over to the right, but the image still is predominantly dark. It still needs some more exposure compensation. This next image shows a compensation of +2/3. Shutter Speed: 1/80 We're getting there - the histogram is now almost centered, and the peak has shifted over to the right. Let's take it one notch further and over expose the image by one full stop. Shutter Speed: 1/60 This is much better - the histogram shows that the majority of the tones in the photo are mid-tones (since the bulk of the chart is in the center of the graph), and it also shows that there are more light tones than dark. You'll notice that the meter is saying that the photo is over exposed by a full stop of light, but it really isn't. The meter has simply been fooled by the overcast light. An under exposed photo like the first one can easily be fixed using any photo editing software, but the goal here is to capture absolutely correct exposures when you take the photo - this means that you'll spend a lot less time later on trying to fix your photos on the computer. In the example above, I used exposure compensation in Aperture Priority mode to intentionally over expose. Another perfectly valid way to do this is to use manual mode, and change either the shutter speed OR the aperture to over expose your photos. Here's how it works: 1. Set your camera to manual mode (M) 2. Select either the shutter speed or the aperture that you want to use 3. Point the camera at your subject and press down halfway on the shutter release button - the camera's light meter will activate and take a reading

8 4. Select the matching setting (aperture or shutter speed) so that the meter is set to zero (correctly exposed, as far as the meter can tell) 5. Take a photo 6. Check your histogram If there is a ANY gap between the end of the histogram on the right side and the far right side of the chart, your photo is under exposed (as illustrated by the red box in the histogram to the right). Since you have the camera in manual mode, you can deliberately over expose your image. Widen the aperture OR slow down the shutter speed by a fraction of a stop (one click of the command dial under your index finger). Take another photo and check the histogram again. You'll notice that the graph has edged closer to the right side of the scale. If the end of the histogram STILL doesn't touch the right side of the chart, keep over exposing the photo until it does. That's when your photo is correctly exposed - based on the lighting conditions. Sometimes you'll have to deliberately over expose by a full stop OR MORE to get the histogram in the right spot. Histograms and Dynamic Range The histogram is a pretty useful tool: it's more accurate than a light meter when it comes to exposure feedback, and it instantly tells you when photos are under exposed, helping you to compensate on the spot rather than having to increase the brightness of your photos with image editing software. And now, for some even better news. A histogram can show you when the dynamic range of the scene your photographing exceeds the limits of your camera's image sensor. Remember our example of the beach at sunset? The camera can either capture details in the highlights OR the shadows, but NOT both. Left in auto mode, it's hard to tell what the camera is going to choose to expose correctly. Unfortnately, switching to manual mode isn't much help, because your meter is going to be thrown off by the extreme contrast. But our histogram - truthful tool that it is - will quickly tell us when there's too much dynamic range in between light and dark for the sensor to handle. It does this by clipping off the histogram on both the right and left sides of the chart.

9 When you see a histogram that's clipped on both sides, it means that there are portions of the photo that are so bright that they appear as pure white (the clipping on the right side of the chart) and other parts that are so dark that they appear as pure black (the clipping on the left side of the chart). Any time your histogram clips on both sides, you've got a photo that's exceeding the dynamic range of your camera. When this happens, you have one of four choices: 1. Decide if you want to expose for highlights or shadows and user your spot meter to set exposure 2. Take the photo from a different angle to reduce the contrast of the light on your subject 3. Wait until a different time of day to take the photo when sun is lower in the sky 4. Use a light modifier called a diffuser to balance the contrast of the light When you use your spot meter to expose for shadows or highlights, then the histogram will only be clipped on ONE side: if you expose for shadows (and let the highlights go to pure white) the clipping will be on the right and if you expose for highlights (and let the shadows go to pure black) then the clipping will be on the left. If you're able to reduce the contrast in the image by one of the three methods above, then the histogram should show no clipping on either side of the chart. Exposure Bracketing The practice of bracketing exposures was a by-product of photographers who didn't have a nifty histogram to refer to. When you bracket exposures, you set up the camera so that it takes three versions of every photo you take: 1. Correct exposure (based on the METER reading) 2. Over exposed 3. Under exposed

10 Zero Over Exposed Under Exposed You have direct control over two parts of this bracketing process: 1. The amount of over and under exposure 2. The order of the three sequential photos Let's talk about #1 first: remember that your metering scale runs from -2 to +2 (with zero in the middle) and that the numbers represent FULL stops of light (where +1 is one full stop over exposed). You can adjust your bracketing range so that the camera is only over and under exposing by a third of a stop (a minor exposure difference), or you can set it so the camera is over and under exposing by 2 full stops (a major exposure difference). You can also typically customize the order in which the photos are taken. For example, you might choose the three photo exposure sequence to be zero, over, under or it could also be zero, under, over or even under, zero, over. But why is bracketing still a feature on digital SLR cameras that have sophisticated light meters and fancy histograms? Natural light comes in an infinite variety of forms: from the muted tones of an overcast day to the hard shadows and strong contrast of a bright summer afternoon. While you can use your meter and histogram to get accurate exposures, sometimes an ACCURATE exposure won't create the most INTERESTING photograph. I periodically will set my camera to bracket when I want to be surprised by the effect that can only be acheived with an over or under exposed image. This technique works especially well for portraits, where a perfectly balanced exposure may not be the most flattering for your subject. ISO ISO is one of the most powerful features on your digital SLR camera.

11 Which brings up the question: if it's such a great feature, why have I waited this long to tell you all about it? The problem is that it's hard to understand the power of ISO is until you have a thorough understanding of exposure, and the limits that you run into when taking photos in dim light. I'll start out by giving you a quick definition, and then we'll dig into much deeper detail. The ISO setting is an indication of the light-gathering capacity of your digital SLR sensor. The higher the ISO number, the more light the sensor absorbs. Like aperture and shutter speeds, ISO numbers follow a common scale: An ISO setting of 100 means your camera's sensor absorbs fairly LITTLE light, while at ISO 3200 it absorbs a LOT of light. ISO numbers are a hold-over from film: when you purchased a roll of Kodak 200 from your local drugstore, that mean that the film was rated as ISO 200. The most common ISO ratings for film were 200 and 400, but you could find some specialty films with ISOs as low as 25 and as high as But here's the big difference and one of the HUGE advantages of the digital camera: you can change ISO on the fly. With film, you had to plan ahead - once you'd loaded a roll of ISO 3200 film, you could not abruptly switch to ISO 100 without taking all the photos on the roll and then popping in a new roll of ISO 100 film in the camera. With digital, you can take one shot at ISO 100, the next one at 3200 and the next at 400. That's what ISO is all about - but WHEN should you leverage it? Before I answer that question, I'd like to review those two boundaries: 1. The maximum aperture of your lens 2. The shutter speed / focal length relationship The first boundary is a mechanical one: your lens can only open up so far and it has a limit to how much light it can let in. The widest opening of your lens is called the maximum aperture. Not all lenses have the same maximum aperture - some open much wider than others. How much wider? Just use the aperture scale to figure that out: A change between each number on this scale either doubles or halves the amount of light entering the camera. This means that a lens with a maximum aperture of f/1.4 lets in double the amount of light of a lens with a maximum aperture of f/2.0, and four times the amount of light as a lens with a max aperture of f/2.8.

12 Let's also refresh our memory about the aperture / shutter speed relationship: WIDER APERTURE --> FASTER SHUTTER SPEED This is why lenses with wide maximum apertures are called "fast lenses". When your lens opens wide and lets in a ton of light, you can use very fast shutter speeds and still get balanced exposures. If your lens doesn't open very wide, then you have to use slower shutter speeds, regardless of the amount of available light. This brings us nicely to the second boundary: the shutter speed / focal length relationship: Shutter speeds slower than 1/focal length of the lens will result in blurry photos when you're holding the camera in your hands and not using a flash (unless you have image stabilization). Let's say that you're taking photos outdoors on a bright sunny day. Under these circumstances, you can use just about any aperture/shutter speed combination you want without having to worry if your photos will turn out blurry. But as the light gets dim, your shutter speed must slow down accordingly to get a correct exposure (the longer the shutter stays open, the more light it lets in). If your shutter speed gets too slow, you run the risk of capturing a blurry subject (due to subject motion) or an entirely blurry photo (due to camera shake). Now that we've done our quick review, let's talk about a specific example where only ISO can help you out. ISO Example Imagine that you're trying to capture a photo of your son or daughter playing quietly (yeah, right) in the living room. 1. You set your camera to manual mode 2. The light is dim - you need all the light you can get into the camera so you set your lens aperture as wide as it will go (f/4) 3. Checking your meter, you find that the matching shutter speed for a correct exposure is 1/8th of a second This won't work. Even if your child is sitting perfectly still, 1/8th of a second is just too slow to avoid some form of blur. Without image stabilization your entire photo will be blurry and with it your child will be blurry but the background will be clear (since it's not moving around). But what to do? You're stuck right? The lens is open as wide as it will go, and there's no way to get MORE light into the camera. ISO saves the day.

13 Each increase in ISO results in a FULL STOP increase in the shutter speed, because the sensor is absorbing more light. Since the sensor is more receptive to light, you don't have to use such a slow shutter speed, and you'll still get a decent exposure. ISO SHUTTER SPEED SAMPLE PHOTO 100 1/ / / /60

14 1600 1/ /250 Look at that! By the time you get up to ISO 3200 you're blazing away with a shutter speed that's fast enough to freeze motion even if your child is JOGGING all over the room. This is why I like to call ISO the low-light booster. In dim light, increasing the ISO also increases your shutter speed so that you can take nonblurry photos. With a simple change from ISO 100 to 800, you'll be able to easily take photos indoors without having to use a flash. This by itself would make the ISO setting incredibly useful. But there are also plenty of other situations where an increase in ISO is going to capture a better shot. Moderate Light, Fast Action Instead of taking photos in a dim living room, imagine that you've taking photos outside on an overcast day: the overcast light is significantly brighter than any indoor light. But there's a catch. You're not photographing your child playing with his or her toys - you're trying to take photos of a horse race. You follow the usual steps to get your camera set up: 1. Start with ISO Set your camera to shutter priority mode 3. Select the fastest shutter speed the camera will allow (given the amount of available light)

15 Let's say that the fastest shutter speed the camera can muster is 1/500th of a second. This is excessive for non-moving subjects, just fine for subjects moving around a bit, and even OK for a subject engaged in robust physical activity. But it's not going to be fast enough to capture clear photos of those horses. We're back to ISO again, even though this time there is quite a lot of available light. A jump up to ISO 200 will let you use a shutter speed of 1/1000th of a second, and an increase to ISO 400 will help you get up to 1/2000th of a second. These shutter speeds should be plenty fast to capture those horses as they tear around the track. Aperture: f/5.6 Shutter: 1/640 ISO: 800 While not a horse, my labrador moves pretty fast when he's chasing after a ball in the backyard. It's afternoon, and the entire backyard is now in shade. I knew that at ISO 100 I wouldn't get a shutter speed fast enough to freeze his motion, so I upped the ISO to 800 to get the shot. Aperture: f/5 Shutter: 1/250 ISO: 400 I wanted to capture a photo of this squirrel theiving bird seed. He was moving pretty fast, and the light is overcast. I was also using a 200mm lens, so I increased the ISO until my shutter speed was faster than 1/focal length of my lens. Increasing Depth of Field With ISO Yes, it's true: ISO isn't ALL about shutter speed, even though its most frequent use is when you've got your lens set to its maximum aperture and the shutter speed STILL isn't fast enough for clear photos. Now, if you're dealing with a fast-moving subject, you don't have a lot of options. You'll need to use a shutter speed between 1/500th and 1/4000th of a second to freeze the action so you need the sensor to be absorbing all the light it can. But when you're dealing with a subject that isn't tearing all over the place, you've got some creative leeway to increase your depth of field as you increase your ISO. Let's go back to the child playing in the living room. In this situation the subject isn't moving fast, so there's only one rule you need to apply: your shutter speed must be faster than 1/focal length of the lens (this eliminates the effect of camera shake).

16 Let's review the shutter speeds that I used to photograph my son: ISO APERTURE SHUTTER SPEED 100 f/4 1/8 200 f/4 1/ f/4 1/ f/4 1/ f/4 1/ f/4 1/250 I used a 28mm lens to take the photos. This means that by ISO 400, my shutter speed was plenty fast to get a clear shot (1/30th of a second). I now have two options: 1. Stop at ISO the shutter speed is sufficient for the subject, and doesn't need to go faster 2. Increase the ISO, and increase aperture - this will get me more depth of field in my shot Here's that table again, but rather than increasing the shutter speed, this time I'm going to narrow my aperture (and increase my depth of field): ISO APERTURE SHUTTER SPEED 100 f/4 1/8 200 f/4 1/ f/4 1/ f/5.6 1/ f/8 1/ f/11 1/30 Of course, if your camera or lens has some form of image stabilization, then you'll have even more freedom to play with aperture as you increase ISO, because you won't be limited by the 1/focal length rule. The Catch With all of these benefits, you might be wondering why you can't just set your camera to ISO 1600 and leave it there all the time. As with most good things, there's a catch to increasing the ISO setting on your camera: it also increases the amount of digital "noise" in your photos. Digital noise makes photos look speckled instead of smooth. With film, this speckling was called "grain".

17 Noise is most obvious: In wide areas of matching color (like the sky) In areas of shadow This photo clearly illustrates the effect of digital noise. Noise not only causes colors to appear speckled, it can also disrupt the cleanliness of lines and can make your images appear slightly out of focus. Camera manufacturers have invested a great deal of effort (and money, no doubt) trying to reduce the presence of noise in high ISO images taken with their cameras. There actually is a physical aspect of your camera that does affect the amount of noise in high ISO photos: the size of the digital sensor. The smaller the sensor, the more noise it produces at high ISO. This is why EVERY digital SLR camera generates less noise than every compact digital camera: the sensors on digital SLRs are larger. Despite the fact that all SLR sensors are essentially the same size, every time a new camera is released the online photography discussions revolve around how the camera handles noise at high ISO. Battle lines are often drawn on the topic - many people will swear that their Canon produces less noise at ISO 800 than a Nikon. Cameras aside, the volume of ISO noise in your photos also depends on your photography style, and how often you feel the need to increase the ISO.

18 Simply put, if image quality is of utmost importance to you, then never set your ISO above 200. If you find yourself in a position where a slow shutter speed is going to cause blur, then make sure you have a stable platform - like a tripod - that the camera can rest on. This is what professional photographers have been doing for years. But if you absolutely love taking spontanous photos in dim lighting conditions while holding the camera in your hands, then you will have to accept a little noise in your photos for the increased shutter speeds you can get by using a high ISO. The ISO Chart I've put together the following ISO chart that will help to give you an idea of what ISO setting to use when. Please realize that these are not abosolutes - the ISO setting that you ultimately choose will be directly related to the shutter speed that you need to clearly capture your subject. You only need to adjust your ISO setting when: 1. You're holding the camera in your hands if the camera's attached to a tripod, there's no chance that it will shake and blur your photo so you can use low ISO settings and slow shutter speeds 2. Your subject is in motion if you don't want a blurry subject, you have to use a fast shutter speed 3. You're not using a flash flash adds more light to your subject, which means that you don't need to boost the ISO to get a correctly exposed photo My recommendation: print this chart and carry it around with you. That way when you're faced with changing light, you'll have a sense of where to begin when it comes to your ISO setting. LIGHT SUBJECT SPEED ISO Bright sunlight Slow 100 Moderate 100 Fast 200 Shade Slow 100 Moderate 200 Fast 400 Overcast Slow 200 Moderate 400 Fast 800 Indoors, bright Slow 400 Moderate 800 Fast 1600 Indoors, dim Slow 800 Moderate 1600 Fast 3200 Night Slow 1600

19 Moderate 3200 Fast Good luck Adjusting Color With White Balance The color of light changes dramatically throughout the course of the day. It also changes when the light source switches from natural (sunlight) to artificial (light bulb, fluorescent tube, camera flash). We're not always aware of these color shifts because our eyes automatically adjust. When it comes to color, we really don't see things the same way a digital SLR camera does. Like ISO, the way a digital SLR camera captures colors is very similar to the way a film camera captured colors. Most standard films were what's called "daylight" film - they were designed to capture accurate colors when the light source was natural daylight. But if you used the same film to take photos indoors, you'd get one of two different results: 1. If the the light was tungsten (a regular light bulb) your entire photo would have an orange tint 2. If the light was fluorescent your entire photo would have a pale green tint This is because the temperature of light produced by these two artificial sources is not the same as the temperature of light produced by the sun. The "temperature" (or color) of light is measured in Kelvins. Now that we've got a scale of measurement, we can see in the following table how different light sources (even different natural light sources) produce radically different color temperatures: LIGHT TEMPERATURE (KELVINS) COLOR Sunrise / Sunset 2500 Tungsten 2800 Twilight 3500 Flash 5000 Daylight 6500 Overcast 7000 Shade 7500 Blue Sky 12,000 But if the color of light is constantly shifting, how are modern digital SLR cameras able to capture photos that look natural? Again, the digital SLR has the advantage over its film counterpart: it can automatically adjust a setting called white balance, which compensates for different temperatures of light and makes colors appear natural.

20 White Balance The white balance setting on a digital SLR camera is really not aptly named, since it really controls how the camera's sensor captures COLOR. If you take a closer look a the different white balance settings, you'll notice that they are identical to many of the different lighting conditions that I laid out in the table above: daylight, overcast, shade, tungsten, fluorescent, flash and often a custom setting. Unlike other camera settings like aperture, shutter speed and ISO, white balance is something that you can often leave on AUTO. When you do this, the camera detects the temperature of the light hitting the sensor and sets the white balance so that the colors in your image look natural. But there are two distinct times when you can set your white balance manually: 1. When you DON'T want the colors in your photo to appear natural 2. When the lighting is coming for a variety of sources Color Enhancement The first reason for setting a manual white balance is really an aesthetic one, and subject to your discerning eye as the person taking the photo. An intentionally incorrect white balance setting will produce photos with a distinct color tint. For example, if you set your camera to tungsten white balance but are taking photos in daylight, all of your images will look blue. A more subtle use of the manual white balance setting is when you want to "boost" the colors in your image for a more dramatic effect. Let's say that you're taking some shots of a brilliant purple flower that's completely shaded by a nearby tree. In AUTO white balance mode, you notice when reviewing the photos on the camera's LCD that the colors don't "pop" quite as much as you'd like them to. That brilliant purple flower looks a bit pale. Solution: manually set your camera's white balance to "shade". Now when you take photos of that flower, the camera will be color correcting for the fact that a shaded light doesn't have the same color temperature as direct sunlight. The purple should now appear rich and saturated. You can use this same technique any time you want to enhance the colors in your photos without having to edit them using software. Mixed Light Sources Imagine that you're using your digital SLR to take photos inside a gymnasium, and that the gym has some windows high up on the walls that allow some natural daylight to filter in. That natural light isn't enough for atheletes to see during a basketball game, so the gym also has tungsten lights that light up the floor.

21 If you're taking photos from the stands, your camera's AUTO white balance is going to have a tough time deciding what to do. Every photo that you take will be a COMBINATION of natural daylight and tungsten light, and both of these have very different color temperatures. If you leave your camera in AUTO white balance mode, you'll find that the color in some of your photos turns out OK, while in others it will have a distinct color tint. The images that you take won't have consistent colors because the two different light sources are COMPETING with each other. In this case, the best thing to do is manually set your white balance and take some test photos - checking the results on the camera's LCD - before the game starts. If one light source is more powerful than the other then that's the setting to use. Let's say that the daylight coming in through the windows is not nearly as dominant as the light being put out by the tungsten bulbs. In this case, manually setting the white balance to tungsten will produce consistent natural colors in every photo you take. Conclusion It's the end of lesson three, and hopefully you're starting to feel pretty confident about using your digital SLR. Even if you're not manipulating aperture, shutter speed, ISO and white balance with your eyes closed, you at least know why each feature is useful. At some point in the future, faced with a challenging lighting condition the material presented here should come back to you and help you get the shot you want. So we're done right? That's more than enough camera terminology to cover every possible photo need isn't it? Not quite. There's one more lesson about the technical stuff, but after that you get to experiment with your camera and really have some fun. Exercises EXERCISE 1 - BRACKETING To set your camera to bracket exposures you're going to have to dig into some menus. Since bracketing is not a common need of the average photographer, digital SLRs don't make the bracketing feature easily accessible. Using the menus on your digital SLR, set it up so that you're bracketing your photos by -1 and +1. This means that instead of just one photo, you have to take 3. While the sequence of the images may not be the same on all digital SLR cameras, there will be one that is under-exposed, one that is correctly exposed and one that is over-exposed.

22 Keep the camera in this mode for awhile, and take photos that you have taken before without bracketing. If it's common for you to take shots of flowers in the yard or your cats lounging on the bed then use these same subjects for your bracketing tests. Make sure that you take the same photo 3 times, so that the camera can bracket exposures for each subject. While you won't learn a great deal taking bracketed photos, you will learn a lot when you review the photos on your computer. This exercise will show you that your camera's meter isn't always right. There are many times where a "correct" exposure really isn't the best choice given the photographic subject. An over or under exposed photo may yield much better results (and may be more pleasing to your eyes) that the one that is correctly exposed. This bracketing exercise is also a good opportunity for you to see how a histogram shows you if the photo is over or under-exposed. To get this additional benefit, set up your camera's LCD display so that it displays a histogram in addition to the photo. When you take each shot in the bracketing sequence, watch the histogram change for each one. In the under exposed photo the histogram will peak on the left, correctly exposed it will peak in the center and over exposed will peak on the right. EXERCISE 2 - FUN WITH ISO To really work with ISO, you should be in an environment where there's not a lot of light. The easiest location for an ISO test is your living room. As it turns out, taking photos indoors in the middle of the day in a house with tons of picture windows is not the same as taking photos outdoors. The light falloff inside a house is so substantial that it's hard to get photos that aren't blurry. 1. Set your camera to aperture priority mode and adjust the aperture so that it is as wide as it will go (the smallest f number). This means that the lens is letting in as much light as it possibly can. 2. Make sure that your ISO is set to Check your shutter speed. Depending upon the amount of light in the room, it might be anywhere from 1/15 to 1/60. You can't hold a camera in your hands and get clear shots at 1/15 (unless you're using a lens with a focal length of 15mm or less) and 60 won't do for subjects that are moving around. What to do? You can't open the aperture any further (it's wide open) and you can't leave the shutter open that long without getting blurry photos. Solution: increase your ISO, and increase your camera's sensitivity to light.

23 Change your ISO to 200 and check your shutter speed. Since you haven't changed the aperture, your shutter speed should now be faster. If the new shutter speed still isn't fast enough, keep increasing the ISO until you get a shutter speed you can use. I typically up my ISO when shooting indoors to about 800, which gets me a shutter speed of 125, good for most stationary and slow-moving subjects. Your ISO and shutter speed setting will be different depending upon how much light enters your home, but everyone will benefit from using a higher ISO when taking photos indoors. EXERCISE 3 - WHITE BALANCE This exercise is completely unnatural, but it will show you how changing the white balance affects the color of your photos. The reason that it's unnatural is that you are going to deliberately set the wrong white balance for the scene that you're taking a picture of. Setting the wrong white balance will help you understand what happens when you use the right one. The first part of this exercise happens indoors. 1. Turn on a light with a standard light bulb (called tungsten in the world of white balance) 2. Set your camera's white balance to daylight and take a photo of the light itself, or an object that is lit with the tungsten light 3. Take a photo and check the results on your LCD You should notice that the entire photo has an orange color tint. Even the light itself (if you include it) appears as an orange color rather than white. Now change your white balance to tungsten and take another photo. Colors should look natural again, the way that your eyes perceive the scene in front of you. With your camera still set to tungsten, head outside and take a few shots. Notice the blue tint that is applied to every photo you take? If you change the white balance to daylight (or shade if that's the light you're working with) you'll see objects once again regain their natural color. Finally, find a room filled with fluorescent light and take a few photos with you camera set to daylight white balance. Don't really like the results this produces? Set your camera to fluorescent white balance to correct the colors. IMPORTANT NOTE: If you do decide to fiddle around with your white balance, make sure that you check what it is set to when you start taking photos again. If you forget and leave the camera on tungsten white balance when you're taking photos outside, you're going to be very disappointed with the results.