What is Shutter Speed?
In our last article on Explaining Exposure, we talked about how the shutter speed relates to how long a camera’s shutter stays open to let the light in. We used a water faucet as an analogy to understanding shutter speed. The longer it stays open, the more water (light) pours out and fills the cup (of exposure).
Inside a DSLR camera, there are two metal blades called the shutter curtains. They are called curtains because like window curtains, they open and close to let light in. There is a front curtain that slides open vertically to let light hit the sensor and a rear curtain that closes afterwards to block the light. The length of time in which the curtains stay open is known as the shutter speed.
Shutter speed is also one of the three factors that determine a proper exposure. The other two factors are aperture and ISO. If there is a change to either aperture or ISO, you can adjust the shutter speed to balance out the change in exposure.
Finally, the shutter speed is used as an artistic tool to freeze motion or convey motion in the image.
Shutter Speed from Miguel Yatco Cheat Sheet
Shutter speed is typically measured in fractions of 1 second. This means that when you see 60, 80, 125, etc. in your camera indicator screen, they translate to 1/60th of a second, 1/80th of a second, 1/125th of a second, and so on. The majority of DSLRs top out at 1/2000 or 1/4000 sec, but some of the higher-performing cameras have a maximum shutter speed of 1/8000 sec.
Going the other way in time length, once the shutter speed slows down to 1 second or longer, the indicator will display 1″, 2″, 4″, and so on. Many DSLRs can have a very slow shutter speed of 15″, 30″, or 60″. This means that the camera will continue to let light in for that many seconds.
When the shutter stays open longer and all the other settings remain constant, you are allowing more light in. As a result, the image is brighter. A photo that is taken at 1/60 sec shutter speed will look brighter than a photo taken at 1/200 sec shutter speed.
Each time you cut the length of time in half (ex. 1/100 s to 1/200 s), you are letting half as much light in and the image is “one stop darker.” Each time you double the length of time (ex. 1/100 s to 1/50 s), you are letting twice as much light in and the image is “one stop brighter.”
A stop is a photographic measurement of light that indicates the relative change in the brightness of light. When the exposure is darker by one stop, it is receiving half as much light as before. Conversely, when the exposure is brighter by one stop, it is receiving twice as much light as before.
Most cameras also offer a “B” mode or Bulb Mode either on the Mode Dial or at the end of the Shutter Speed selection. This mode is essentially a manual shutter mode, where the shutter curtains will stay open as long as you hold the shutter button down, and will only close when you release that button. Therefore, you can actually leave the shutter open for minutes to even hours if needed.
An example of when you want to use the Bulb Mode is for night sky photography, where you would leave the shutter open for many minutes to record the star trails. The reason you want to do this is because the stars in the night sky emit such a low amount of light that in order for the camera to effectively see it, the shutter must be open for a long time.
The word Bulb actually refers to the old days of photography where the camera shutter is held open by a rubber bulb attached to the camera via a shutter cable. The photographer would squeeze the bulb to keep the shutter open and then would release it to close the shutter.
Besides for dialing in the “proper exposure,” you can use the shutter speed to creatively freeze or show motion. A relatively fast shutter speed freezes motion, which is great when you want to capture someone jumping in the air without creating any motion blur.
A slower shutter speed is used when you want to convey motion. This gives a sense of dynamic direction and makes the object looks like it is really moving. In the example below, the exposure time is 13 seconds. This made it look like the cars were moving so fast that they were only leaving light trails behind them.
One of the consequences of a slow shutter speed is that the sensor will start to pick up any camera vibrations that can occur while the shutter is open. This tends to happen when you are hand-holding the camera instead of securing it on something more stable like a tripod. There is rule of thumb called the reciprocal rule that states that whatever is your lens’ focal length, that is the slowest shutter speed that you should shoot at without introducing any shaky blur into your shot. So for example, if you are shooting with a 200mm lens, you want your shutter speed to be at least a 1/200 sec or faster.
There are several ways to help you shoot at a slower shutter speed:
- Place the camera on a tripod or a secure stationary object.
- Improve your camera holding technique to help you be more stable if you can’t use a tripod or a stationary object.
- Use a lens that has an in-lens stabilization feature like the Canon 24-105mm IS USM lens or a DSLR with an in-body stabilization feature like the Pentax K-30 DSLR.
So to recap, the shutter speed is the measurement of how long the camera shutter stays open to allow light to hit the sensor. It is measured in fractions of a second up until 1 second and then measured in whole seconds for longer exposures. You use it in conjunction with aperture and ISO in order to get a proper exposure. You also use it as an artistic tool to freeze or convey motion in a photograph.
Finally, if you are using a shutter speed that is a slower value than your lens’s focal length, be sure to stabilize your camera in order to minimize unwanted blur.
That’s it for the basics of shutters speed. Next, we are going to talk about the basics of aperture and ISO.