Photography is all about light. Literally. When you think about how a camera works, it’s not unlike how your eye works. Light is reflected from a subject, passes through the lens and the pupil and then hits the back of your eye where it activates tiny cells in the shapes of rods and cones…your brain does the rest. We don’t normally think of objects and people reflecting light (unless they’re shiny), but that’s what’s happening (if you don’t believe me, hit up your high school physics teacher on facebook and ask them).
So, if photography is all about capturing the light reflected off of the subject, the camera is all about controlling the amount and quality of light that eventually hits the film or sensor. At the most basic level, there are three factors that determine how much light gets processed:
- shutter speed
So i’m going to make some posts about shutter speed, ISO and aperture, and how they work and interact to properly expose your shots.
Of the three, shutter speed is probably the easiest concept to understand, especially if you know how a SLR (or DSLR) works. In an SLR, light enters the lens in the front, travels through lens elements(groups of individual lenses), through the aperture to the camera body. In the camera body, as long as you don’t press the shutter release, the light hits a mirror and is reflected up into the viewfinder – hence the name single lens reflex – your camera only has one lens, and it reflects the light from that lens to the viewfinder for you to see what the lens sees.
Wikipedia has a diagram that might explain it better.
Before SLR’s, you had a separate lens or window to look through in order to compose your photo. Anyway, when you press the shutter release, the mirror lifts up, and the shutter opens and closes. The rate at which the shutter opens and closes is called the shutter speed. It acts like a gate, allowing a time period during which light can pass through and hit the film or sensor. Because of this, you’ll see shutter speeds listed as times – most often fractions of a second – 1/60 is one sixtieth of a second. 1/125 is one, one hundred twenty fifth of a second, and so on. The slower the shutter speed, the more light is going to hit your film or sensor.
You want to dial in your shutter speed based on the amount of action in your shot. If you’re shooting someone standing still with little movement, then you can probably shoot at 1/60th. But if you tried to use that same shutter speed on a moving bike or a car, you’re going to get a blurry shot, since the bike rider or car will have moved in the frame during the time the camera’s shutter was open. In these examples, you’ll want to use a shutter speed of at least 1/500th and probably 1/1000th or 1/1500th. The quicker the shutter speed, the more action it’s going to freeze. You’ll want to experiment with moving subjects to find the shutter speed sweet spot.
Long exposures are typically made over a period of 1 or more seconds. These types of photos are mostly made at night, and they’re how you get those long trails of tailights in photos of roads. Most cameras have at least a few shutter speeds in whole numbers like 1″, 2″, 5″ and those correspond to whole seconds.
Each of the following photos were exposed for 5 seconds. In the one on the left, the lights didn’t move. In the one on the right, the lights were in motion.
You may also see a b setting on your shutter speed selection – that stands for bulb. This setting acts as a toggle – press the shutter release to open the shutter, and then again to close it – how long the shutter stays open depends on you. You may be wondering why bulb? It goes back to when camera shutters were operated by a little bulb that you squeezed that would pump air into the shutter mechanism to operate the shutter. They looked (and worked) like the bulb on a blood pressure cuff.
Speaking about long exposures, if you’re taking a long exposure shot, you’ll not only want to use a tripod (moving the camera around is like having the subject move around) but you’ll want to avoid actually touching the camera to open and close the shutter. There’s even a risk of you moving the camera as you press the shutter release and therefore making a blurry image. There are several ways you can avoid this: using a cable release (that physically screws into the shutter release), a remote control (either infrared or radio) or just by using the timer function built in to almost every camera.
You can experiment with shutter speeds by putting your camera in shutter priority mode. In this mode, you have control of the shutter speed, and the camera makes adjustments to the aperture and ISO in order to expose the images as best it can.