Achieving correct exposure is about getting the appropriate amount of light through the lens and on to the photo sensitive material inside your camera - whether that material is film, or glass, or tin, or paper, or a digital sensor, or whatever. Too much light and the photo will be over exposed (too light/washed out), not enough light and your picture will be under exposed (too dark/muddy shadows).
There is quite a lot of information in Parts 1 through 5, here is a quick summary:
Part 1: FORGET ABOUT THE DAMN EXPOSURE TRIANGLE
The exposure triangle is bollocks. ISO has no influence on the creative aspects of a photo and really isn't part of exposure - it should be regarded differently and not as a part of the so-called exposure triangle. Only increase ISO when it isn't possible to capture an exposure with your preferred shutter speed and aperture.
Part 2: EXPOSURE VALUES
There are always several different combinations of shutter speed and aperture that will produce the same, or equivalent, exposure value.
Increasing shutter speed by one stop and reducing aperture by one stop will maintain the same EV. The opposite is also true - decreasing shutter speed and increasing aperture by the same amount will not affect the EV.
- 1/1000" at f/2.8
- 1/500" at f/4
- 1/250" at f/5.6
- 1/125" at f/8
- 1/60" at f/11
- 1/30" at f/16
All have the same exposure value provided they are shot at the same ISO.
Part 3: SHUTTER SPEED
A fast shutter will freeze motion.
A slow shutter will blur motion.
The faster an object is moving the faster your shutter needs to be to capture it sharply. The more slowly an object is moving the slower the shutter needs to be to cause it to blur effectively.
For action, sports, fast moving objects: minimum of 1/500"
For people, stationary things: 1/60" - 1/250"
For very low light, panning, to create blur: 1/30" - 30", bulb, timer
Part 4: APERTURE, DoF, AND BOKEH
A wider aperture (small f number) will produce a small Depth of Field (DoF) while letting more light pass through the lens.
A small aperture will produce a deeper DoF but let in less light.
Apertures smaller than f/16 will progressively lose sharpness due to diffraction.
Landscapes: deep depth of field, smaller aperture f/8 - f/16
Environmental portraits/objects: shallow DoF, large aperture f/1.4 - f/4
Studio portraits/objects, architecture, highly detailed objects: your lenses sweet spot, sharpest setting. Usually around three stops closed from the maximum aperture.
Starbursts: small aperture f/16 - f/27
Part 5: MEASURING THE LIGHT
Choose the most appropriate metering method for the scene you are capturing.
Matrix/Evaluative Metering: averages the amount of light over the entire image with some weighting given to the area around the focus point. It will average the brightness of the image to middle grey or Zone V. This method works well in evenly lit scenes.
Centre Weighted Metering: ignores the focus point and averages light values closer to the middle of the frame. Works well for tight portraits and subjects that fill most of the frame. Also works well for back-lit subjects.
Spot Metering: measures the light in one area only, around the focus point. Spot metering is useful if there are large areas of light or dark in the scene. Hand held spot meters can produce very accurate exposure readings by measuring the luminance of exposure zones individually.