Our last technical discussion was about shutter speed to control the freezing of motion or showing the blur of motion. This one will be about aperture. Part 1 will discuss how it works.
Aperture and shutter speed work together to form two points of the Exposure Triangle. ISO speed is the third point (can you guess what the next technical post will be about?)
How the Aperture Works
The aperture of the camera lens works exactly like the iris of your eye. It opens wide to let more light in, it closes down to let less light in. In this way, the lens controls the amount of light allowed to enter the camera hitting the sensor. Whereas shutter speed controls the amount of time the light is allowed into the camera.
Think of this easy way to keep them straight: Aperture is the amount of light let into the camera; shutter speed is the length of time that light is let into the camera.
Another way to think about it is to picture filling a water glass in your kitchen sink. The glass represents the perfect exposure when it’s filled. If you turn the faucet on full blast (wide open aperture) how long does it take to fill the water glass? Not long (fast shutter speed).
If you turn the faucet on at a trickle (small aperture) how long does it take? A lot longer (long shutter speed) either way, the glass gets filled (the perfect exposure), it’s just a matter of how much water (light) and how much time (shutter speed). Got it?
Aperture and Shutter Speed Work Together
So, aperture and shutter speed work together to make the correct exposure your camera’s computer is telling you it needs.
Aperture is expressed in f-stop numbers. The f-stop is a mathematical formula expressing the ratio of the lens focal length to the diameter of the aperture. Did I lose you? No worries –keep reading. It’s complex and way more than you need to know –but if you really want the nerdy details here’s a link to the Wikipedia article f-stop telling you more than you ever wanted to know about how f-stops are derived. While I may have found this article very interesting, you may be in danger of hurting yourself by dozing off and falling out of your chair.
What you only really need to understand is this: A small f-stop number (i.e. f-2.8) is a large aperture; a large f-stop number (i.e. f-16) is a small aperture. The f number works in the opposite direction as to the size of the aperture. Most people find this confusing and I think the founding fathers of photography set it up that way because first and foremost they were scientific nerds –and secondly they never envisioned us mathematically challenged everyday people to ever get our hands on one of their magic boxes.
To sum up
When wide open, the aperture lets in more light as in dark lighting conditions; when closed down it lets in less light as in bright daylight conditions. The amount of light entering the lens is offset by the amount of time that light is allowed to enter the lens (shutter speed) to create the perfectly exposed shot.
However, just like shutter speed does more than control the amount of time light is allowed to enter the camera, so does the aperture. As you may recall, a fast shutter speed stops motion, a slow shutter speed shows the blur of motion. So it goes with aperture –there’s more to it. Come back for my next post Aperture Part 2 for the effects a wide and small aperture have on your pictures.