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Photographic technique has been covered in extreme detail in many other publications and Web sites. However, it is my firm belief that to take good pictures on a consistent basis requires a firm understanding of some basic photographic technical concepts.
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EXPOSURE
Probably the most important concept in photography is exposure. Exposure is simply controlling the amount of light that reaches the light-sensing element in the camera. In modern (digital) cameras, the light-sensing element is usually a CMOS electronic photo-sensor. In film cameras, the light-sensing element is good old film. Whether it's a CMOS circuit, a CCD circuit, or film, I will simply refer to it as a "sensor" - since it's the element that "senses" (and records) light. Exposure is the means of controlling the amount of light that reaches the sensor.
Exposure can be controlled in two ways: By varying the amount of light transmitted through the lens (aperture or f-stop), and by varying the amount of time the sensor is exposed to the light source (shutter speed). The smaller the lens aperture (higher f-stop numbers), the lesser the transmitted light allowed through the lens. Likewise, the faster the shutter speed, the lesser the amount of light exposed to the sensor.
To further complicate the issue, the sensor (film or digital) can have more or less sensitivity to light. This sensitivity is measured in ISO numbers. A doubling of the ISO number equals a doubling of the sensor's sensitivity to light. ISO was called ASA in the old days, and for you old-timers, the numbers are identical. Digital camera ISO settings are typically 100 or 200. Film ISO sensitivities range from 64 to 800. For now I'm going to leave ISO out of the discussion...
Both shutter speed and aperture increment in factors of 2. In other words, one f-stop doubles (or halves) the amount of light reaching the sensor. Likewise, one increment in shutter speed halves (or doubles) the amount of time the sensor is exposed to light. Just to confuse the issue, most modern cameras allow you to adjust both f-stop and shutter speed in on-half or one-third increments, therefore needing two or 3 increments to achieve a "full stop" of exposure change.
Since both aperture (f-stop) and shutter speed are selectable, it's important to understand their relationship. A typical "sunny day" outdoor photographic scene may have an optimum exposure of f16 at 1/100 (one one-hundredth of a second). This means the camera settings can be f16 @ 1/100, f8 @ 1/200, f5.6 @ 1/400, f4 @ 1/800, f2.8 @ 1/1600, f22 @ 1/50, etc. For every optimum exposure, there are literally dozens of f-stop and shutter speed combinations that will result in the sensor receiving the correct amount of light.
Determining the correct exposure for a given scene can be a difficult task. However, modern cameras do an amazing job of determining the optimum exposure for almost any scene that the lens may be pointed at. That being said, the camera may be "fooled" by a scene that may be predominantly light (e.g. winter & snow scenes), or dark (e.g. night scenes). It's up to the photographer to add exposure compensation as necessary to increase exposure (lighten/brighten the scene) or decrease exposure (darken the scene).
As a quick example, if a photo is being taken of a winter/snow scene and the photographer uses the in-camera exposure meter, the resulting image will have snow that's medium grey, rather than white. To get white snow, the photographer should increase the camera's exposure reading by 2 full stops - this means "opening up" the lens by 2 f-stops, or slowing the shutter speed by a factor of 4.
In the "good old" days, before we could afford light meters (and cameras with built-in meters), we used the "Sunny f16 Rule". The sunny f16 rule meant that the optimum exposure for an outdoor scene was an aperture of f16 and a shutter speed of the inverse of the film ASA (now ISO). So, with ISO 100 film loaded, the optimum exposure for a sunny outdoor scene is f16 at 1/100. Modern digital cameras have variable ISO settings - but all digital cameras have a "native" ISO (typically 100 or 200). The "Sunny f16 Rule" can still be applied! Find out the native ISO of your digital camera and then wander outside on a sunny day. Set the camera to manual mode and select the shutter speed as the inverse of the ISO (1/100 or 1/200 for most cameras). Set the lens aperture to f16 and shoot away. You'll be surprised how close to "perfect exposure" this simple system is.
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ISO
ISO is simply a measure of how sensitive the sensor is to light. The higher the ISO number, the more sensitive the sensor becomes. In other words, the higher the ISO number, the less light is required to obtain an optimum exposure.
With film, the photographer chose ISO 400 or 800 film for working in low-light situations. Likewise choosing ISO 64 or 100 film for working in daylight. The problem with high ISO films is "grain". Images produced from high ISO films gave what should be a smooth, uniform surface a "rough", "sandy", or "grainy" texture. In some cases the "grainy" look is desirable - part of the "photographic art" if you will, but in most images, grain is bad.
With today's digital cameras, the photographer can simply dial in the desired ISO and shoot. High ISO settings still result in "grainy" images, but in the case of digital it's due to electronic noise in the camera circuitry rather than the chemical composition of the film.
That being said, high ISO performance has leapt ahead in previous years. My Nikon D700 takes quite acceptable images at ISO 3200 - something unheard of as little as one year ago! Digital camera manufacturers will continue to "push the boundaries" of high ISO performance. I have no doubt that ISO's will hit the 10,000+ mark in the next 2-3 generations of digital cameras.
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APERTURE
Why would a photographer want to change the aperture of the lens? Why not simply fix the aperture at a given setting and vary the shutter speed and ISO settings to obtain the optimum exposure? The answer is something called Depth of Field (sometimes called depth of focus).
Depth of Field is defined as the area of the image that's in "sharp" focus in front of, and behind the focus point of the lens. A "shallow" or "narrow" depth of field means that very little of the image is sharp in front of, or behind the object the lens is focused upon. A very common use of shallow depth of field is to blur background objects in the image that may otherwise be distracting. To obtain a shallow (or narrow) depth of field, the photographer must use a large lens aperture (or low f-stop number). Shooting a scene at f2 or f2.8 will certainly result in a shallow depth of field.
To achieve a "wide" or "long" depth of field, the photographer must use a small lens aperture (high f-stop number). Scenic landscape images and architectural images are two good examples of images that usually require a wide depth of field. Shooting such a scene at f16 or f22 will result in a wide depth of field.
There are mathematical formulae that calculate depth of field for any given situation, and many photographers carry depth of field calculators while on a shoot. I prefer to experiment by shooting scenes at multiple apertures and using the depth of filed preview button on my camera. After all, once you've invested in a digital camera (and accessories), additional pixels are free!
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SHUTTER SPEED
Why would a photographer want to change the shutter speed of the camera? Why not simply fix the shutter speed at a given setting and vary the aperture and ISO settings to obtain the optimum exposure? The answer is has to deal with motion - both subject motion and camera motion.
Hand-holding a camera is a difficult thing. The human body shakes, quivers, sags, and twitches at all times. To hand-hold a camera "rock steady" is in fact impossible. No matter how steady your hands may be, the fact is you must move at least your finger to activate the shutter release! This movement is translated to at best an "unsharp" image, and at worst a total blur. By using a high shutter speed, the motion created by the human hand can be "cancelled out". In short, it is possible to hold the camera steady for a very brief time. What's the "magic time" you ask? If you're using a camera with a full-size 35mm sensor, the "rule of thumb" is that your chosen shutter speed must be at least the inverse of your lens focal length (or faster). In other words, if you're using a 80mm lens, the slowest shutter speed you should attempt (while hand-holding the camera) is 1/80 of a second. If the camera sensor is smaller than 35mm, you need to multiply this by about 1.5 - making the slowest shutter speed for our 80mm lens now 1/120 of a second.
Camera manufacturers have started to assist photographers with hand-holding their cameras by implementing sophisticated systems that "cancel out" small movements the photographer may make while hand-holding the camera. These "image stabilisation" or "vibration reduction" systems can be integrated into the lens and/or camera body. Manufacturers claim that these systems allow the photographer to hand-hold their cameras at as much as 4 stops slower than the "rule of thumb" speed. Our 1/80 of a second from above now becomes 1/5 of a second. I don't put that much faith in these systems, but through experimentation I can safely say that a 2 stop increase is certainly achievable (making our example of 1/80 of a second into 1/20 of a second).
The other motion to consider is subject motion. Sports photographers are well known for using fast shutter speeds to "freeze" their subjects in mid-motion. Likewise, other images may actually display some "motion blur", giving the viewer of the image a sense that the object was indeed in motion. Modern cameras have shutter speeds up to 1/8000 of a second (and faster). That's not fast enough to "stop a speeding bullet", but it will certainly stop almost any motion found in nature.
Fast (or short) shutter speeds tend to "freeze" or "stop" subject motion, while slow shutter speeds result in motion blur. An outdoor photographer photographing a waterfall or stream may use a fast shutter speed to freeze the water droplets in place, or use a show shutter speed to make the water droplets appear as a blurred "curtain" of water. Which is better? That's difficult to judge. Every scene can benefit from either stop-action or motion blur. Since pixels are free, I usually tend to take both photos.
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TRIPOD
After the purchase of a camera body & lens, the next purchase should be a high-quality, sturdy tripod. No other accessory can assist you to take better images than a tripod. A tripod "slows down" the photographic process, allowing the photographer more time to contemplate the image composition as well as adjust aperture, shutter speed, ISO, etc. for the desired exposure. The tripod also allows the photographer to use long shutter speeds that would be impossible when hand-holding the camera. A sturdy tripod will guarantee "razor-sharp" images every time!
A tripod should be strong, steady, and light-weight. Very few "consumer" tripods fit this description. I suggest looking at professional-grade tripods and picking one that makes sense for your shooting style. It will be a larger investment (in both money and time), but it's an investment you only have to make once. Bottom line - buy a professional level tripod and you won't be sorry!
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THE REST OF THE KIT
Once you've acquired a camera body, lens, and a sturdy tripod, go forth and shoot! As your technique improves and you gain experience, you'll add accessories to your photographic kit. Filters, lenses, carry bags, electronic flash, and remote releases are just a few of the literally hundreds of photographic accessories out there for you to choose from. Don't worry about them now - get out there and get some images! As time goes by you'll realize what you need and don't.....
