I am taking this information and reposting it from a website www.digital-photographey-school.com. Great website for learning the basics. I like the way they talk about the relationship of ISO, aperture and shutter speed in this posting. Once you get an understanding on how they work together it will help to bring you photography to the next level. I hope they don’t mind me reposting this. I did include the links so it should help to bring more traffic to their site. I always want to give credit to the original maker.
Many people describe the relationship between ISO, Aperture and Shutter Speed using different metaphors to help us get our heads around it. Let me share three. A quick word of warning first though – like most metaphors – these are far from perfect and are just for illustrative purposes:
Imagine your camera is like a window with shutters that open and close.
Aperture is the size of the window. If it’s bigger more light gets through and the room is brighter.
Shutter Speed is the amount of time that the shutters of the window are open. The longer you leave them open the more that comes in.
Now imagine that you’re inside the room and are wearing sunglasses (hopefully this isn’t too much of a stretch). Your eyes become desensitized to the light that comes in (it’s like a low ISO).
There are a number of ways of increasing the amount of light in the room (or at least how much it seems that there is. You could increase the time that the shutters are open (decrease shutter speed), you could increase the size of the window (increase aperture) or you could take off your sunglasses (make the ISO larger).
Ok – it’s not the perfect illustration – but you get the idea.