In photography, exposure is the amount of light which reaches your camera sensor or film. It is a crucial part of how bright or dark your pictures appear. It is often referred to as Exposure value (EV)
Getting the right exposure is essential, we don't want photos that are over or under exposed. Thankfully the camera has an internal metering system and does a pretty good job of getting the correct exposure without interference from us. For any photograph, there is only one mathematically correct exposure. However, if we want to experiment with settings then there are lots of different combinations of Aperture, Shutter Speed and ISO that can be used to create that exposure. They rely on each other, change one and he camera will change one of the others to compensate. Below we look at what each one does and how the settings can be changed.
This is known as the 'Exposure Triangle' and the combinations we use are dependent upon the amount of light available and what we want to achieve from the photograph.
Aperture is the hole in your lens, it controls how much light is let in. The bigger the aperture (hole) (smaller number) the more light is let onto the camera sensor
The Shutter is the curtains that covers the sensor, and the shutter speed refers to how much time the sensor is exposed to the light, longer exposure = more light. Typically Cameras have a range of 1/8000th of a second - 30 seconds.
ISO basically tells the camera how bright to make the image, the greater the number the brighter the image, allowing faster shutter speeds or smaller apertures.
Typically a range is from 50 - 12800
The correct exposure is a combination of the three areas above, that is governed by the amount of light available ( EV Exposure Value) but we can adjust these values and the reason we want to do that is because each of them has a secondary effect, which is where the creative element in photography lies. These changes are often referred to as 'stops'.
Aperture also controls depth of field, (DoF) - This indicates how much of the scene is in focus, The bigger the aperture, (f2.8)the smaller the DoF, The smaller the aperture (f32) the greater the area of the picture in focus.
The other consideration is that most lenses are at their 'best' at about f8 - f16
Shutter speed also controls the 'motion' visible in the photograph, the faster the shutter speed (1/500th) all motion will appear to freeze in the picture, this is useful for sports photography, a slower speed (1 Sec) motion will blur, useful for waterfalls.
The other consideration is that a tripod is required for slower shutter speeds - the golden rule is never hand-hold a camera at a shutter speed less than the lens in use I.E. if using a 135mm lens, never hand-hold less then approx 1/125th
ISO governs how bright the image is, but the pay off here is, as the ISO increases, so does the amount of 'grain' in the picture. Grain is seen as speckles or 'haze' in the picture.
The question is if higher ISO causes grain why use it?
2 Reasons really, 1 is for artistic effect (dark moody pictures), 2 is because you can use faster shutter speeds - When I was photographing Whales in Iceland - I had to up the ISO to 1600, to get the shutter speeds i needed otherwise (given the light) the Whales would be blurred.
Two other ways of adjusting the exposure in and programme mode are Bracketing and Exposure compensation, for more information see the camera manual, as and when you want/need to use them.
Exposure Compensation is a method of adjusting the exposure value by up to 3 stops, in the programme modes you can you this to under or over expose the shot. You can also use manual mode (M) which can do the same.
Bracketing is a useful feature, which allows you to take multiple shots and each one varies the exposure or WB etc, slightly with each shot. Something to explore as and when you need it.