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Photography Basics Question?

I've read online photography tutorials, but I'm still confused about some things, namely exposure values (EV), shutter speed, aperture, and flash? Aren't EV's, aperture, and flash the same thing? What difference does it make if the shutter speed make if it's set to a high or low level (don't know the proper term). I couldn't find "AF," so what is "AF"? And finally, what are EV, shutter speed, aperture, flash, and AF in relation to each other?

Thank you so much!
My digital camera has Multi, Center, 0.5m, 1.0m, 3.0m, 7.0m, and an infinity-like symbol (∞) settings for AF.

NOTE: This answer is, of necessity, rather long. Reading it more than once is advised. If there were any other way to answer I would.

In the olden days EV (Exposure Value) had an entirely different meaning and use than it does today. Today its used as an expression of Exposure Compensation.

Suppose you're photographing a snow scene or a beach scene with white sand. If you depend on your camera's meter to determine the exposure your white snow/sand will be a shade of grey instead of white. Why? Because your camera's meter "sees" everything as represented by 18% grey - the reflectance of an average scene. If we know this, then we know that we have to "help" the camera make a correct exposure by adding +1 or even +2 EV. With your digital camera you can easily see the effect and then make any needed adjustments - perhaps +1.5 EV instead of +2 EV. In effect, we are deliberately overexposing the scene to get the results we want - white snow/sand. NOTE: EV only works in either Aperture Priority or Shutter Priority. In Manual Mode it has absolutely no effect.

The aperture - aka f-stop - is an opening formed by the movable blades of the diaphragm inside the lens. It controls how much light is actually admitted. A large f-stop - f1.4, f2 - admits a lot of light. A small f-stop - f8, f11, f16 - admits very little light with f16 admitting the least.

The shutter speed controls how long the light admitted by the f-stop chosen is allowed to expose our film or digital sensor. The ISO we've chosen also plays a role. (ISO is simply a measurement of the sensitivity to light of a light sensitive surface, film or sensor. A low ISO, 50, 100, is very insensitive and requires a lot of light. A high ISO, 200, 400, 800, is more sensitive and requires less light).

Here is an easy way to see this ISO/f-stop/shutter speed relationship: the old "Sunny 16 Rule". It was invented back when cameras didn't have a built-in light meter and states: "On a sunny day, set your aperture to f16 and your shutter speed to 1/ISO." So lets set an ISO of 100 and go out on this sunny day.

ISO 100
f16 @ 1/100 sec.
f11 @ 1/200 sec.
f8 @ 1/400 sec.
f5.6 @ 1/800 sec.

See the pattern? As we "open up" our lens (f16 to f11 to f8 to f5.6) we admitt more and more light. With more light admitted, our shutter speed increases to compensate. Less light = slower shutter speed, more light = faster shutter speed.

If we shoot in Aperture Priority (we set the f-stop) the camera will select a shutter speed to give a correct exposure based on the ISO and f-stop we selected.

If we shoot in Shutter Priority (we set the shutter speed) the camera will select an f-stop to give a correct exposure based on the ISO and shutter speed we selected.

If we shoot in Manual then we must manually change the shutter speed when we change the f-stop or change the f-stop when we change the shutter speed. So what happens if we don't? A bad exposure. Try this and prove it to yourself. Go to Manual Mode and set f16 and use 1/800 sec. shutter speed. Your result will be a black image - underexposed. Now set f5.6 and use 1/100 sec. shutter speed. Your result will be a white image - overexposed.

"AF" usually stands for "Auto Focus".

"Multi" AF would be used for a group of people.

"Center" AF would be used if your subject was the single most important object and you weren't concerned about any other object.

The "Distance Scale" - 0.5m, 1.0m etc. allows you to set a predetermined zone of focus. This can be useful if your goal is to control Depth of Field (DOF). For a good explanation of DOF, go here:

http://www.dofmaster.com/dofjs.html

Your flash is for those situations when there is insufficient light and your camera simply cannot make a correct exposure without help from an artificial source - the flash.

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