Ok first things first, the exposure of an image is dictated by 3 elements (the exposure triangle), shutter speed, aperture and the ISO setting. The process of a photo being taken is the shutter opening and closing, light coming in through the lens and shining on the sensor inside your camera.
With the above in mind lets talk about shutter speed and aperture first. Shutter speed is how fast the shutter opens and then closes again when you push the trigger, These shutter times can range anywhere between 1/8000th of a second and 30 seconds.
The aperture is is the size of the hole in the lens that will allow the light through the lens and onto the sensor, this is either changed manually or will be done automatically depending on the camera setting. Aperture settings typically range from 2.8 to 22, these values are shown as F numbers, i.e. F2.8 or F22, the smaller the number the larger the hole in the lens that lets light in.
If we assume the amount of water to fill a bucket to the brim is the amount of light we need for a correct exposure. We can also assume the size or diameter of the hosepipe is the aperture and the time to fill our bucket with water or light in the case of a photo is the exposure time.
What we have now is a lot of options as to how we fill the bucket or expose our image correctly. We could use a fire hose to fill the bucket (large aperture F2.8) for a very short period of time 1/8000th of a second or we could fill the bucket through a straw (small aperture f22) for a very long time say 30 seconds. So as you can see there is no magical number or setup, it really depends on what you are trying to photograph and in what conditions.
Here are some scenarios for you;
Sports Photography normally has to have a fast shutter speed to freeze action so based on the bucket analogy we would need a large hosepipe or aperture (f2.8) so we could fill the bucket quickly (fast shutter speed) this will ensure we get enough light on the sensor for a correct exposure. With an aperture of F2.8 we have a very shallow depth of field so the background to our subject will be blurry which for this application is preferred.
Landscape Photography tends to use a large f number say F22 (small hole) as everything needs to be in focus which is the opposite to our sports shot, we don't want anything blurry for our landscape image. So a small aperture or small hosepipe means the bucket will take longer to fill i.e. we need a longer shutter speed say 1/30th second.
The ISO value is how sensitive the sensor in your camera is to light, ISO 200 means it is not very sensitive to light where as ISO1600 means it is very sensitive. The downside to using high ISO settings is that you will start to see noise artifacts in the image, the plus is that it does allow you to shoot in conditions that you normally could not.
A good example of using a high ISO setting would be if we were hoping to do Wedding Photography in a church, there would normally be very little light in this situation. We would therefore need to have a small aperture F2.8 (large hole) to get the maximum light onto the sensor. We may find though that the camera still needs a slow shutter speed and maybe too slow to hand hold and not get a blurry picture. Increasing the ISO will make the sensor more sensitive to light and therefore allow you to use a faster shutter speed, meaning you can hand hold you camera and not get a blurry image whilst still correctly exposing the image.
I hope you enjoyed this article and if you have any questions at all I would be only happy to answer them for you, below are links to my website should you wish to look at my work.
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