Understand Your Digital SLR

When they were first introduced, digital SLR cameras were enormously expensive and a tool for professionals only. Since then, they have come down in price into the consumer price range. Because of this, many people buy digital SLRs without understanding how they work -- and, consequently, not making the most of them. This article will guide you through the most common functions they have, and show you how to learn to use one by experiment. The principles are the same for any camera, but you will probably not be able to set your shutter and aperture manually on most non-SLR cameras. Scroll past the jump for more information.

Steps

  1. Look for a subject. We're going to be taking photographs at a wide range of settings, so it's important that you don't take photographs of anything too dark. Remember that human sight can perceive a much wider range of light intensities than a digital camera sensor (which is referred to as the camera's dynamic range). We can look through a window and still see what is inside at the same time, even though the light conditions inside are totally different from these outdoors. Cameras, and especially digital cameras, cannot. So on camera, you will only see what's outside through the window or what's inside. Consider this when picking your subject.
  2. Steady your camera. If you have a tripod, use one; if you have a solid surface to rest on, then do so. Not that a tripod is as necessary as many people say it is; but to observe the effects of various camera settings, it's best if you get several shots of exactly the same thing. Tripods really come in handy for slower shutter speeds. Most pictures go bad because of a camera shake. Though as mentioned above, if your lens has an automatic stabiliser, use it....
  3. Set your camera to fully-automatic mode, generally designated Program (P) mode. On some cameras, there is also an auto-ISO (sensitivity) mode to set separately in order for the camera to choose that automatically. Some cameras or lenses have a switch to choose among manual focus and one or more auto-focus modes. Generally you will want auto-focus, with the mode that checks for perfect focus before taking a picture (generally "single shot"). Manual focus is helpful for low light and other conditions where the auto-focus gets confused; "continuous"/"tracking"/"AI Servo" auto-focus mode, which follows (what it thinks is) the subject continually as the shutter button is partly depressed to reduce delay before clicking all the way is best for sports and other fast-moving subjects.
  4. Play with your camera's ISO speed. This will be the first camera setting that you will experiment with. You can set this in the camera's menus; many cameras will allow you to change this with a couple of button presses, too. The ISO speed is a measure of your camera's sensor's sensitivity to light; a lower number is less sensitive, and a higher number is more sensitive. Take a photo of your subject at its lowest ISO speed (or "slowest", typically 50, 100 or 200), and then take one at its highest (800, 1600 or more). Observe the following:

    • The photo taken with the slower ISO speed will have forced the camera to use a slower shutter speed (which we'll get to later on), while the photo taken with the faster ISO speed will have used a faster shutter speed. The difference between the two may have been significant enough to be audible. Being able to use a faster shutter speed means that you can, for example, freeze motion (and also avoid camera shake) in poorer light than you could with a slower one.
    • The photo taken with the slower ISO speed will have less noise (random discoloured pixels) than the one taken with a faster ISO speed (although digital SLRs, owing to their larger sensors, have much better high-ISO performance than small point-and-shoot digital cameras do). Hence, you're left with a trade-off between image quality and usability in low-light conditions. At a concert, for example, a higher ISO speed may well be more appropriate; in bright daylight, or when you're using a tripod and--even better but not critical--a remote release too, lower ISO speeds may be more appropriate.
    • Use the minimum ISO speed that allows an adequate shutter speed (generally 1/focal length for handheld pictures, one or two stops slower with image stabilization, faster such as 1/250 for action or sports) and an adequately small aperture to have all important detail elements (such as people) within the depth of field. This will often be a pretty high ISO. No matter -- a few discolored pixels here and there is much, much better than pervasive defocus or motion blur smearing the image or large parts of it across many, many pixels. Some cameras can automatically pick a reasonable ISO.
  5. Set your camera to aperture-priority mode for a moment. We'll get around to exactly what this means in a second. For Canon, it's called "Av" (for Aperture value) on your mode dial. For Nikon, it's called "A".
  6. Set your lens' aperture (also called the diaphragm). This might be a dial on your lens with a series of numbers on it (which will typically fall anywhere between around 1.4 and 22 on most lenses); otherwise, refer to your camera's instructions. The diaphragm is just that: an opening towards the front of your lens that lets more or less light onto the sensor. The size of the diaphragm is expressed as a ratio of focal length to aperture size (hence, they are referred to as, for example, f/5.6); consequently, a smaller aperture (less light onto your sensor) is expressed by a larger number. So, take two photographs, one with a larger aperture, and then stop down and take one with a smaller aperture. Observe:
    • The background of your subject is less sharp with a larger aperture than it is with the smaller one. This is called the depth of field. So, if you want to make a subject stand out from the background, use a large aperture to blur the background; if you need to get more of your scene in focus, use a smaller aperture. Some lenses have pairs of lines that will fit around different distances on their focusing scales to show what range will be fairly sharp at a given aperture. (The area outside of that range will be more blurred the further outside it is, but less blurred at small apertures than at large ones.) Because defocus depends on the angle at which light rays diverge from the object to enter the lens, it increases more rapidly the closer something is to the lens -- focusing on something, say, twenty feet away with a typical lens will put objects from several feet away to infinity more or less in focus, while focusing on something one foot away will put only that which is very close to one foot away in focus.

    • The smaller aperture lets less light onto the sensor than the larger one would have, forcing the camera to compensate for this by using a slower shutter speed. This is what "aperture priority" exposure control is about. In automatic mode, the camera will adjust either the aperture or the shutter speed to get the right amount of light onto the sensor; Av mode forces the aperture to take priority and the camera will only adjust the shutter speed. However, this means you won't see the effect of the changed aperture in Av mode on overall exposure, because the camera would have automatically compensated for it. So try setting your camera into fully manual mode (M) to see the effect of the aperture on light.
    • Hence, there is a trade-off between depth of field and low-light performance. You can either have a wide open aperture, which will give you little depth of field but plenty of light onto the sensor, or a smaller one, which will do the opposite. There are also problems with diffraction effects stealing sharpness at very small apertures; as a general rule, don't use one smaller (remember: larger number!) than f/8 or f/11 unless extreme depth of field is really needed.[1]
  7. Set your camera to fully-manual (M) mode. This will tell the camera to give up all control of trying to expose your picture properly. Most of the time, you will not need to use this (and shouldn't; exposure control exists for a reason). But we'll need to do this if we're going to show the effects of shutter speed.
  8. Play with your shutter speed. See your manual for the exact details of how to do this. Shutter speeds are numbers which go up in a sequence that roughly doubles each time, and normally expressed as a fraction of a second; i.e. 1 second, 1/2, 1/4, 1/16, 1/25, and so on (each one usually being called a "stop"). Take two pictures at shutter speeds a couple of stops apart. Observe:
    • The photo with the fast shutter speed will be darker. This can either be a good or bad thing, depending on lighting conditions.
    • The photo at the slower shutter speed might show some motion blur if you were holding it by hand. Even if you're setting your camera on a tripod, at very slow shutter speeds (of half a second or more, such as one would use at night), you might see some blur because of camera shake.
    • Hence, in very dark conditions, you will need to use a slower shutter speed; but such slow shutter speeds can cause motion blur. In brighter conditions, you will need to use a faster shutter speed, which will have the effect of freezing motion. This can be a good thing or a bad thing. If you need to get a longer exposure during the daytime, use an ND filter.
  9. Memorise these things. Think about it in terms of light; you can adjust either your aperture, ISO speed, or shutter speed to compensate for various strengths of light. Adjusting either of them will have effects on your image, for better or for worse. Memorise these effects, and for a time, think about these things while you are taking photographs, until they become second nature.
  10. Put your camera back into Program (P) mode for now. It's nice to know the above things, and in time you'll learn when to use each of time. Most of the time, Program mode will be sufficient.
  11. Play with different lenses, if you have them. If you don't, the chances are good that you have a zoom. Either is fine. Fixed lenses of different sizes have different focal lengths; zoom lenses have a variable focal length. The focal length is the distance in mm between your lens elements (the glass inside) and your film/sensor. The perspective you get is completely different for each focal length.
    • The standard 50mm lens is more or less equal to the sharp central field of view of human sight, if they are paired with 35mm film or a full-frame sensor. However, be aware that most digital SLR sensors are smaller than regular 35mm film. Therefore, your effective focal lengths are multiplied by about 1.5 on most digital SLRs (this is called "FOV cropping"). Most of Canon's sensors have a 1.6 crop factor. Most Nikon DSLRs have a 1.5 crop factor.
    • Wide-angle lenses, like a 28mm, lets you fit a lot of the scene onto your sensor. It has a wide view. It also creates the impression that you are looking at your object from a distance. It therefore is good for taking pictures of small rooms (makes these look bigger), landscapes, etc. Things near the edge of the frame will appear stretched. This is interesting for buildings, but weird for people. Wide-angle lenses make the subject look big only when it is very close to the lens, but still take in a wide area of background. When the general background, such as a sweeping view, is interesting, a wide angle lens is good. When a small part of it, such as a colorful sunset near the horizon, is interesting, a telephoto lens and moving back is good.
    • The telephoto lens, like 80mm or longer, will bring things closer to you. Therefore, this is used for portraits (because it forces you to be further away from the subject; the perspective at longer distances makes noses appear smaller), and wildlife photography. However, bear in mind what was said about apertures earlier; for a long telephoto lens to let in the same amount of light as a smaller lens, it has to be a lot larger. An extreme 200-500mm f/2.8 zoom lens, for example, weighs nearly 35 pounds, and is still nearly twice as slow as the 50mm lenses of 30 years ago.[2] Short of these kinds of extremely expensive lenses, most consumer grade telephoto lenses tend to be slow (i.e. its aperture in relation to the focal length will be relatively small compared to that of a smaller lens), forcing you to use longer shutter speeds if it is in a low-light situation. This can be compensated for by using faster ISO speeds, as described above; this is a trade-off you have to make. (Wide aperture lenses require a lot more money and have a lot more weight; it's often actually better to get the cheap ones that will be taken out and used even if that involves a little more noise from a high ISO setting. The cheap ones are basically just as good at apertures such as 5.6 and smaller which are usually desirable for significant depth of field. For shallow depth of field, one can use an expensive very-wide-aperture lens, or simply use a longer-focus moderate-aperture lens and move back until the subject is the same size.)
  12. Zoom lenses can have distortion--making straight lines not straight, typically curved--particularly at the extremes of their zoom ranges. Some cameras can automatically alter the images to compensate. If yours doesn't, try to avoid placing long straight lines close to parallel to the edges of the frame where this is likely to be a problem.
  13. Get out and take pictures. Now that you have a better understanding of how your camera works, and how to use it in situations that your camera cannot do automatically, you need to get outside and start using it.
  14. A flash has several uses. SLRs generally can automatically control output of their internal flash, or an external flash with much higher maximum power, to provide even light across a subject. Use a flash at reduced power (applying negative "flash exposure compensation") in sunlight to soften but not eliminate shape-defining shadows. Use a flash in dim light to light the scene. Bouncing a flash off the ceiling (with an external unit with a hinged head) will softly light a large area. A flash is very brief so the part of an exposure coming from it is basically determined by aperture and ISO setting, not shutter speed (which is generally limited to 1/250 or slower due to the way a "focal plane" shutter common in DSLRs works). A slower shutter speed makes the scene's ambient light more conspicuous but don't use such a slow shutter speed that the ambient light can blur the scene due to camera shake or subject movement over a long exposure.
  15. A polarizing filter -- get a "circular polarizer" for best compatibility with autofocus lenses -- is useful under sunlight to reduce glare and brighten colors by reducing reflected sunlight, particularly making the sky dark blue. Rotate it in its mount for maximum effect. Cheap ones can be fine, but check that they are coated (or multi-coated) to reduce reflection spots in the image and that the threads are not poorly cut, which could damage the threads in the lens--particularly if the filter threads in the lens are plastic.
  16. Often you will want to have your camera produce finished JPEG format files rather than (or in addition to) unfinished but fully manipulable RAW format files. One part of the camera's processing of the raw image data is to adjust the colors so that the brightest, fully reflective, objects appear white rather than the true yellowish or bluish colors of light they reflect under incandescent light or open sky (and everything else appears to have the mix of colors it would under the sunlight our eyes are calibrated for). That is what the White Balance (WB) setting does. Automatic white balance (AWB) often doesn't work well; a setting for the kind of light most prevalent in the scene such as sunlight (flash and shade are about the same as it), incandescent, or fluorescent light helps. Some cameras can calibrate themselves to any color of light by first directing you to photograph a known white surface under that light; precisely how to do this is a more advanced subject.

Tips

  • Keep your camera in Program mode until you are proficient in other modes. This mode allows the most flexible option for you to favor shutter or aperture based on the creative results determined by shutter or aperture choice. Depth of field or action? Think motion or sharp detail. Shifting the P exposure is easy and fluid. Use semi-manual mode Tv (shutter priority for Canon DSLRs) or S (Nikon and other DSLRs) if the light is changing and you need say, 1/1000th of a second for sports action; use Av (aperture priority) when you want to pull a scene into focus with f/22 and the sun is playing hide and seek behind a cloud or if you want an out of focus background. Manual mode gives you the most control. Keep in mind a digital camera has 30 plus aperture and shutter settings, so be patient and persistent in Manual mode. Learn how to use your light meter in manual mode with the help of your camera's manual. Learn how to use a histogram to determine if you blew the highlights out or completely lost the details in shadows.
  • Some cameras have a two second self timer function. This is very useful when taking very slow shutter speeds (above one second) as it eliminates the camera shake caused by pushing the 'take photo' button.
  • If you find you need to take photographs of unmoving objects (such as a city skyline) at night, using a tripod will allow you to use a lower ISO setting by keeping the camera still during longer shutter speed exposures. This can allow you to take beautiful nighttime shots without a less noticeable amount of noise.

Related Articles

Sources and Citations

  1. ↑ See Ken Rockwell's page on diffraction; also see the more in-depth article including the mathematics of the problem.
  2. ↑ See Ken Rockwell's review of one of these lenses.
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