I understand shutter speed but what confuses me is ISO and Apeture. The Apeture is physically the opening which determines how much light comes in , but ISO determines how sensitive the camera is to exposed light.
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Think of a photo like a painting, only instead of putting paint on a canvas, you put light onto a piece of film (or a digital sensor).
When you’re painting, you can use different things like bigger or smaller brushes, thicker or thinner paint, heavier or lighter brush strokes to change your painting, but how do you do that with light?
You control it through shutter speed, ISO and aperture.
Shutter speed is how long the shutter is open. If the shutter opens and closes really quickly, then only a bit of light gets in and the picture is dark. If it opens for a long time then a lot of light gets in and makes the picture brighter.
Aperture is the size of the hole that the light goes through to get to the film. A bigger hole means more light and a brighter picture. A smaller hole means less light and a darker picture.
ISO is simply how ‘sensitive’ the film is to that light. Much like how quick a canvas can soak up paint. The more sensitive the film, the more light stays on the film.
Now all three work together.
If you need more light, you can either :
Open the shutter for longer
Make the aperture bigger
or use a higher ISO.
Please note this is a very simple explanation of what the three things do. There are other things to think about beyond this ELI5, like subject movement, noise and depth of field etc.
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