Ok so here's a rough overview of some theory.
Amongst a whole bunch of other stuff, taking a photo is about finding a balance between three things, ISO, Aperture and Shutter speed, the relationship between these three things and how they work is called exposure. Any change in one of the above three elements will have a specific effect to how the two unchanged elements are affected in creating the photograph.
|The exposure triangle; a balance between ISO, aperture and shutter speed.|
ISO: Basically the ISO is how light sensitive the camera is. The higher the ISO number, the more sensitive the image sensor in your digital camera is, or the more sensitive your film is to light in a film camera.
In professional studio shoots where a room is full of light, you can use a low ISO of 100, the lower your ISO is the better quality your film will be.Where as in a low light situation, for example an indoors sport event, where you want to capture someone in action, increase you ISO to about 800 (or more), doing this will also increase your shutter speed ability so you can capture clear movement.
Tip: In situations where you can't use a flash like a museum, concert or church, increase your ISO.
*It's important to take note that the higher your ISO is, the more susceptible the photograph is to looking grainy.
|ISO comparison; notice how the image in the top left of the frame with an ISO of 100 is a lot sharper and clearer than the image in the bottom right frame with an ISO of 3200. For a magnified look go here.|
The smaller the f-number (for example f-2), the larger the diameter of the hole, and therefore the shallower the depth of field. Small f-numbers are great for close-up profile pictures, because only the face will be in focus, everything outside of the face will be out of focus, which creates a really great effect.
The higher the f-number( say f-22), the smaller the diameter of the opening and the greater the depth of field. High f-numbers are great when you're trying to take a landscape photograph and you want everything to be in focus, not just one aspect of the picture.
*So here's the part that gets a bit confusing a small f-number of say f-2 is called a LARGE aperture, where a large f-number of say f-22 is called a SMALL aperture. I guess that it's logical to think that a lower number would be called small, and a higher number would be called large, but because the hole at the back of the lens is its widest when the f-number is its lowest we call small f-numbers large apertures.
|The first picture was taken using a large aperture, hence the narrow depth of field, resulting in only the daisy being in focus. In the second picture a smaller aperture is used, increasing the depth of field and increasing the amount in focus in the picture.|
Shutter speed: This term is pretty self explanatory. Shutter speed is the speed of the shutter on your camera. Shutter speed is measured in fractions of a second, and measures the amount of time the shutter is open for, each time you take a photograph.
Shutter speed can change the way that movement appears on a camera. Extremely fast/short shutter-speeds can freeze fast moving subjects, for example a propeller on a helicopter making it look like the helicopter is floating in the air (making it look unnaturally frozen). Alternatively slow/short shutter speeds can be used to intentionally create a blur in the picture, this way the propeller on the helicopter will not be clear and frozen in time, but rather blurry, indicating that the helicopter is moving.
The slower the shutter speed is the easier it is to create unwanted movement with hand shake, if your shutter speed is very low, use a tripod or stable foundation to prevent unwanted blur.
Tip: For anything slower than 1/60th of a second use a tripod to prevent hand shake
|The picture on the right is using a fast shutter speed, so we see a sort of frozen snapshot of the water. The picture on the right was taken with a much slower shutter speed and indicates the movement of the flowing water.|