A number of people are buying SLR's these days and we all want to make the most of our expensive new cameras. Unfortunately just getting started can be a daunting task. When you cut through all the terminology jargons, photography is as simple as it was 50 years ago or may be even simpler. Once you understand the basic elements of exposure and how they relate to each other rest of the details just fall into place. The three basic elements you need to understand are Aperture, Shutter Speed & ISO
The Aperture controls the lens’ diaphragm, which controls the amount of light traveling through the lens to the film plane. The aperture setting is indicated by the f-number, whereas each f-number represents a “stop” of light.
The Shutter Speed indicates the speed in which the curtain opens then closes, and each shutter speed value also represents a “stop” of light. The shutter speed is measured in fractions of a second.
ISO ratings determine the image sensor’s sensitivity to light, each value of the rating represents a “stop” of light, and each incremental ISO number (up or down) represents a doubling or halving of the sensor’s sensitivity to light.
A camera's aperture setting controls the area over which light can pass through your camera lens. It is specified in terms an f-stop value, which can at times be counter intuitive because the area of the opening increases as the f-stop decreases. In photographer slang, when someone says they are "stopping down" or "opening up" their lens, they are referring to increasing and decreasing the f-stop value, respectively.
Every time the f-stop value halves, the light-collecting area quadruples. There's a formula for this, but most photographers just memorize the f-stop numbers that correspond to each doubling/halving of light. f-stop numbers like f1.4, f2.0, f2.8, f4, f5.6, f8, f11, f16 & f22 are all standard options in any camera, although most also allow finer adjustments, such as f/3.2 and f/6.3. The range of values may also vary from camera to camera (or lens to lens).
For example, a compact camera might have an available range of f/2.8 to f/8.0, whereas a digital SLR camera might have a range of f/1.4 to f/32 with a portrait lens. A narrow aperture range usually isn't a big problem, but a greater range does provide for more creative flexibility.
A camera's aperture setting is what determines a photo's depth of field (the range of distance over which objects appear in sharp focus). Lower f-stop values correlate with a shallower depth of field.
A camera's shutter determines when the camera sensor will be open or closed to incoming light from the camera lens. The shutter speed specifically refers to how long this light is permitted to enter the camera. "Shutter speed" and "exposure time" refer to the same concept, where a faster shutter speed means a shorter exposure time.Shutter speed's influence on exposure is perhaps the simplest of the three camera settings: it correlates exactly 1:1 with the amount of light entering the camera. For example, when the exposure time doubles the amount of light entering the camera doubles. It's also the setting that has the widest range of possibilities.
Shutter speed is a powerful tool for freezing or exaggerating the appearance of motion. With waterfalls and other creative shots, motion blur is sometimes desirable, but for most other shots this is avoided.
Therefore all one usually cares about with shutter speed is whether it results in a sharp photo — either by freezing movement or because the shot can be taken hand-held without camera shake.
How do you know which shutter speed will provide a sharp hand-held shot? With digital cameras, the best way to find out is to just experiment and look at the results on your camera's rear LCD screen (at full zoom). If a properly focused photo comes out blurred, then you'll usually need to increase the shutter speed, keep your hands steadier or use a camera tripod.
The ISO speed determines how sensitive the camera is to incoming light. Similar to shutter speed, it also correlates 1:1 with how much the exposure increases or decreases. However, unlike aperture and shutter speed, a lower ISO speed is almost always desirable, since higher ISO speeds dramatically increase image noise. As a result, ISO speed is usually only increased from its minimum value if the desired aperture and shutter speed aren't otherwise obtainable.
Common ISO speeds include 100, 200, 400 and 800, although many cameras also permit lower or higher values. With compact cameras, an ISO speed in the range of 50-200 generally produces acceptably low image noise, whereas with digital SLR cameras, a range of 50-800 (or higher) is often acceptable.
When these three elements are combined, they represent a given exposure value (EV) for a given setting. Any change in any one of the three elements will have a measurable and specific impact on how the remaining two elements react to expose the film frame or image sensor and how the image ultimately looks. For example, if you increase the f-stop, you decrease the size of the lens’ diaphragm thus reducing the amount of light hitting the image sensor, but also increasing the DOF (depth of field) in the final image. Reducing the shutter speed affects how motion is captured, in that this can cause the background or subject to become blurry. However, reducing shutter speed (keeping the shutter open longer) also increases the amount of light hitting the image sensor, so everything is brighter. Increasing the ISO, allows for shooting in lower light situations, but you increase the amount of digital noise inherent in the photo. It is impossible to make an independent change in one of the elements and not obtain an opposite effect in how the other elements affect the image, and ultimately change the EV.
The most practical advantage to digital photography is that it costs next to nothing to experiment with the camera’s controls, so go out there and shoot away. You want to become increasingly proficient with all three elements of the exposure triangle, so that you can make adjustments on the fly and know exactly what the resulting effect is going to be.