F-Stop - this controls the size of the opening (or aperture) in the camera. The lower the F-Stop, the wider the aperture is open. For lower F-Stops, more light comes into the camera, for higher F-Stops, less light comes in. The F-Stop also affects
depth of field, which makes the background blurry in close up shots of flowers. Lower F-Stops have less depth of field, so only part of the picture will be in focus. Higher F-Stops have greater depth of field, so nearly the entire picture will be in focus. Read more about depth of field here:
Depth of Field
Shutter speed - this controls how long the shutter is open to allow the camera to capture light. The longer the shutter is open, the more light enters the camera. And of course, the less time the shutter is open, the less light enters the camera.
F-Stop and Shutter speed combine to determine how much light comes into the camera when you click the "doohickey" to take a picture. This is referred to as
exposure. Photos without enough light (too dark), are
underexposed. Photos with too much light (too bright) are
overexposed.
Light meter - most cameras have a built-in basic light meter, typically with numbers like:
-2...-1...0...1...2
This provides a good (not great, but good) idea of how much light is coming into the camera, i.e.
exposure. You typically want to be right around the 0, although the built-in meter is really just a guideline, and should not be relied upon for determining proper exposure. A better way to determine lighting
before taking a picture is to use a hand-held light meter in front of the object that is the focus of the photograph, but that isn't always easy to do.
You can check the results by viewing the picture after you take it on the built-in LCD (on Canons, Sonys, etc). The Canon EOS cameras (and others, I'm sure) also have a
histogram option. The histogram provides graph-based feedback on the brightness levels of the photograph. A nice discussion of histograms can be found here:
Understanding Histograms
In very bright conditions, you will end up using both a high F-Stop (small opening or aperture) and a very short Shutter speed, to keep from getting too much light in the camera.
ISO (film speed) - Digital cameras don't use film, but they do usually have an ISO setting which emulates the corresponding film speed. The standard ISO setting for general purpose photography is 400 or so, higher values let you shoot with less light, but tend to add noise. I use a lower setting (200) for my nature photos to get richer color with less noise. A good discussion of ISO can be found here:
Film Speed Rating - ISO/ASA
