Welcome to day six in the “Creative Christmas” series.  Today we’re going to be tying together everything we have learnt over the last few days on shutter speed, ISO and aperture to learn how to create the perfect exposure.

Basically, the exposure determines how light or dark the image captured by your camera is going to be.

This is usually talked about in stops and without going into the mathematics of it the simplest way to understand what a stop is that it means doubled or halved.

So if somebody says that an image is underexposed by a stop, it means it needs double the amount of light.

There is usually a little green bar on the inside of your camera viewfinder, marked with -3 to +3, which is called a light meter – this will help you understand where your exposure needs to be.

Each of the three controlling factors for your exposure can be adjusted to help you get enough light on the sensor and these all have their own different way of measuring the amount of light they let hit the sensor.

For your shutter speed, it is measured in fractions of a second, so 1/250th means one two-hundredth of a second, so half that to 1/125th and it will let in double the amount of light as the shutter is open for the double the amount of time.  

Conversely, double it to 1/500th of a second and your camera will let in half the amount of light i.e. you have darkened the image one stop.

Your ISO is basically your camera sensor’s sensitivity to light.  

So if you start at 200 ISO and halve it to 100 ISO you reduce the sensitivity of your sensor by a half and have darkened the image by a stop.  Now, say we want to increase the exposure by three stops.

We have to increase the ISO from 200 to 1600, by doubling 200 three times i.e 200 to 400, 400 to 800 and 800 1600.

Finally, your aperture works in exactly the same way, so if you start at f5.6 and need to add a stop of light you would go to f4, likewise if you needed to decrease the light by two stops you would go to f11.

So as a working example, say your settings are 1/125th, ISO 100 and f8 and you need to increase your exposure by two stops, you can do this in a multitude of ways.

Increase your ISO to 400, reduce your f-stop to f4, reduce your shutter speed to 1/30th or any combination of the above, for example, up your ISO to 200 and reduce your f-stop to f5.6 and will have exactly the same effect.

It is important to keep in mind the negatives of changing each setting, which have been outlined in the previous videos – such as depth of field – when making your decision, but just go out and play with the settings and see what effect each of them has on your camera’s exposure.

Tomorrow we’re going to be covering what I consider the only other essential piece of kit after your camera and your lens which is a solid tripod.

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