Join Date: Aug 2007
Location: Knee deep in the pow
I would add two very important items to the list.
This is a throw-back name to the days of film, when you commonly had ISO100, 200, 400, 800 and 1600. There were others, but these are what you would most commonly find in the grocery store. The lower the ISO number, the less sensitive the film was to light. So an ISO 25 is the least sensitive to light, requiring more open aperture (smaller f/stop number) and slower shutter speeds.
In a modern digital camera, the ISO setting is setting the sensitivity of the CCD or CMOS sensor. Again, the lower the ISO number, the less sensitive. So you might think "hey, I'll just run at ISO 1600 all day". Well, there are trade-offs.
Until recently, ISO's over about 800 in digital produced images with splotchy color (called grainy by some, in reference to how old high-ISO film shots looked, but that's not an accurate term for digital). What you see here is the noise in the signal processing as the camera strains to amplify the signal seen by the sensor (CCD or CMOS). Newer CCD's and COMS have a more advanced technology (which I won't embarrass myself by trying to explain), which coupled with advancements in signal processing allow much higher quality images at higher ISO settings. I'm not as familiar with the Canon lines, but the Nikon D300, D700 and D3 all have very advanced systems for dealing with low light. I believe the high end Canon platforms have similar systems.
All this means that if you are shooting in low light, (say an indoor graduation) with a 200mm lens, f/2.8 and 1/60, ISO 100, and you've been asked not to use a flash (not that you probably have one that would help in an auditorium) and the image is just too dark, you can raise your ISO number in an effort to brighten the image. It is usually better to raise the ISO value than to try and brighten a dark image in post processing, but that is a topic for more advanced photographers.
Many people choose to leave this in auto, but I think that is a terrible mistake. White balance gives me as much creative control of my images as any other setting on the camera. White balance simply tells the camera what is supposed to be white, and everything else is scaled from there.
Back in the days of film, you had to either select a film for your application, or use a filter to adjust the lighting coming into the camera. As a beginning photographer, it's important to know that not all light is created equally. Your typical light bulb has a very severe yellow tint to it. Fluorescent lighting has a very blue hue. Flash? Different still. Sunny day? This is considered to be true "white light" by most, having an equal concentration of each color of the spectrum.
If you take a picture that is illuminated by an incandescent lamp, and you have your white balance set to fluorescent, the image will appear very yellow. The camera will try and shift the color spectrum to yellow, because you told it the light source is very blue. Since the light source is already very yellow, it makes the problem that much worse.
If you take a picture in an office, where everything is illuminated by fluorescent lamps, and you are set for incandescent (regular light bulb) it will all be very blue.
If you are set for auto white balance, the camera does an OK job picking out the light color, but the camera still has to guess what is supposed to be white. If you don't have a good range of color in the picture, the camera may not guess right. I don't use auto white balance, ever.
Many cameras have additional settings for white balance. One is where you can set the color of your light source (expressed in degrees Kelvin, or K). A typical number would range from 2500k to 10000k. The higher the number, the more blue the source. Lower, more yellow. Another common setting is a pre-defined white balance. In this case, you take a picture of a white card under your light source, effectively telling the camera "this is white today". This is a very useful setting if you are shooting in controlled light, such as a studio.
Most importantly, don't be afraid to play with these settings. In many posts when people ask "which camera is right for me" I encourage them to go and hold them, see what is comfortable. At the same time, I tell them to see how easily they can adjust shutter speed, aperture, ISO and white balance. I adjust ISO and WB almost as often as I do my shutter and aperture, and I have a lot of fun playing with white balance. I personally like to make my images in my camera, not in photoshop.
1999 e46 328i Ti Silver / Black[retired]
2007 e90 335xi Jet Black / Black[retired]
2011 e70 X5 35d Vermillion Red / Cinnamon
2011 e92 M3 LeMans / Fox Red extended