Every Tuesday, I bring you a tidbit of information to help you improve your images, learn more about the technical aspects of photography and generally just “talk shop”. This week is about understanding Aperture and Shutter Speed.
Images are created by recording the amount of light that falls onto the film or the digital sensor of a camera. The lens of the camera gathers the light reflected off a subject, converges it at a point on the focal plane, inverts the image and the light travels to the sensor of the camera, creating an exposed image of the subject.
Aperture: A camera lens has not only glass we see at the front of the lens but also an aperture that narrows and widens to control how much light enters the lens. The aperture is like the iris of our eyes–a bigger aperture lets more light in, a smaller aperture lets less light in.
The shutter: Look at the image above and imagine there is a door immediately in front of the camera sensor. By controlling how long that door (the shutter) is open, we can control the amount of time the film/sensor is exposed to the light coming through the aperture. Like a door of a house being open to the outside world, the longer the shutter is open, the more light is cast on the film/sensor.
How Aperture and Shutter Speed work together: The best way I’ve ever heard this described is in John Hedgecoe’s The New Manual of Photography. Hedgecoe writes: “The exposure process is like filling a glass with water. The glass is the film (or digital chip) and the water is the light. To fill the glass (expose the film), the faucet is turned on partially or fully (the aperture)–the amount affects how long the tap needs to run before teh glass is full (the shutter speed).” In other words, a wider aperture requires a shorter shutter speed to correctly expose the image in the camera; a narrower aperture requires a longer shutter speed.
Next Tuesday, we’ll talk about the affects you can get from having a wider or narrower aperture.