What is ISO?

You may see a setting on your camera saying "ISO" and there will be various numbers such as 100, 200, 400, 800, 1600 etc. ISO denotes how sensitive your camera's image sensor is to the amount of light present.

ISO speed affects the shutter speed and aperture combinations that you can use on your camera to obtain the correct exposure for an image (so it isn't over or under exposed).

By choosing a higher number ISO, you will be able to use a faster shutter speed, and because a higher ISO means that the image sensor will be more sensitive you will be able to take pictures in low light situations that may not be possible with a low ISO. If there is not enough light present to allow a scene to be correctly exposed with a low ISO and you do not want to use flash then you would need to select a higher ISO. However, the higher the ISO, the more noisy (grainy) the photo will be when it is printed out and the file size will be smaller.

In order to obtain the best image quality, you should select the lowest ISO possible for the conditions.

What is Shutter Speed?

You will hear a lot about shutter speed when learning about photography. This basically refers to how fast the shutter on your camera opens and closes in order to let in the light. By selecting different shutter speeds you are able to freeze or blur movement. Most compact cameras do not have the option to change the shutter speed, but you have full control on an SLR camera.

Short shutter speeds are used to freeze fast moving objects and can be used very successfully in sports photography.

Long shutter speeds are used to blur a moving object to create artistic effects such as making waterfalls appear misty.

Most SLR cameras have a shutter speed range from 30 seconds to 1/4000 second. Each increase in shutter speed is called a "stop" and they double in size. For example, 1/250 second to 1/500 second is one stop and 1/500 to 1/1000 is one stop. Most modern SLR cameras allow the user to have more control, enabling you to increase or decrease the stops by half or a third of a stop. By choosing the Shutter Speed Priority setting on your SLR you can control the shutter speed and the camera will do the rest.  

What is Aperture?

Aperture is another word that you will hear a lot about. The aperture is the size of the hole that lets the light into the camera through the lens. The aperture is shown on your camera as an "F" number (these are called stops), eg F12 or F6. The larger the F number, the smaller the aperture is (smaller hole), the smaller the F number, the bigger the aperture is (bigger hole). The aperture you choose will determine the depth of field.

A large aperture (small F number) will create a small depth of field. This means that the background will be out of focus and the main object in the foreground will be all in focus.

The smaller the aperture is (larger F numbers), the larger the depth of field will be. This means that the whole of the photo from foreground to background will all be in focus.

Aperture and shutter speed work together and your SLR camera will have settings for Shutter Speed Priority and Aperture Priority. By choosing Aperture Priority, it allows you to determine the depth of field, and the camera will set an appropriate shutter speed to make sure the light is right to correctly expose the photo. If you choose a large aperture (small F number) then the camera will pick a fast shutter speed.  If you choose a small aperture (large F number) then the camera will choose a slow shutter speed as it needs longer for the light to enter the camera's sensor.