The three elements are:
ISO - the measure of a digital camera sensor’s sensitivity to light
Aperture - the size of the opening in the lens when a picture is taken
Shutter Speed - the amount of time that the shutter is open
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.
Another way that a friend recently shared with me is to think about digital camera exposure as being like getting a sun tan.
Now getting a suntan is something I always wanted growing up - but unfortunately being very fair skinned it was something that I never really achieved. All I did was get burnt when I went out into the sun. In a sense your skin type is like an ISO rating. Some people are more sensitive to the sun than others.
Shutter speed in this metaphor is like the length of time you spend out in the sun. The longer you spend in the sun the increased chances of you getting a tan (of course spending too long in the sun can mean being over exposed).
Aperture is like sunscreen which you apply to your skin. Sunscreen blocks the sun at different rates depending upon it’s strength. Apply a high strength sunscreen and you decrease the amount of sunlight that gets through - and as a result even a person with highly sensitive skin can spend more time in the sun (ie decrease the Aperture and you can slow down shutter speed and/or decrease ISO).
neither metaphor is perfect but both illustrate the interconnectedness of shutter speed, aperture and ISO on your digital camera.
NB: A third metaphor that I’ve heard used is the Garden Hose (the width of the hose is aperture, the length that the hose is left on is shutter speed and the pressure of the water (the speed it gets through) is ISO.
written by digital-photography-school