Exposure triangle – Shutter speed
Welcome to the third article in the discussion of the exposure triangle. In the two previous articles we discussed ISO and aperture, and in this article we’ll be talking about shutter speed. Out of all the parameters that make up the exposure triangle, shutter speed is probably the easiest one to understand. Most people know that a camera is simply a closed box with a lens that allows light to come through and record the image onto a sensor or film. The shutter is simply a mechanism much like a door that opens and shuts to let the light in and then to stop the light.
A shutter curtain that opens to expose the sensor and record the image[/caption]
That door is called a shutter. the shutter is actually made up of two parts. These parts are the first curtain and the second curtain. When you’re not taking a photograph, the shutter is closed so that no light can come into the camera. When you press the shutter button to take a picture, the first curtain (which is actually covering the sensor from the light) swings up to open and let the light flow through to the sensor. The second curtain will now swing up and cover the sensor once again. The longer the shutter is open the brighter the image. This is probably the easiest and most common way to determine the brightness of a photograph.
The amount of time that the shutter is open and letting light through to the sensor is called the shutter speed. The shutter speed is measured in seconds or fractions of a second. This value can be changed depending on how much light there is in the environment. In a darker environment you will have to have a longer shutter speed such as 1/30th of a second. If you’re in a really bright scene you may have to turn up the shutter speed to a much faster speed such as 1/400th of a second. Of course this depends on your other settings such as ISO and aperture which we’ve discussed in the previous articles but we will talk about how to bring the three components of the exposure triangle together in the final article. For now, all you need to understand is that the shutter is simply an electronic door that opens and shuts to let light in. The other thing to remember, is that while the shutter is open the sensor is going to record everything that it sees. This might sound like an overly obvious thing to say but you need to understand this in order to be able to predict what your photograph is going to look like. Let’s say for example, that you are photographing a racing car. If you do not use a shutter speed that is fast enough for it to freeze fast movement, then your photograph is going to appear blurry or shaky. The reason for this is that if the subject is moving too fast , the camera is also going to record that movement resulting in a blurry photograph. This is one year going to have to consider what the final image should look like. Perhaps you do want some motion blur in your photographs to indicate or highlight the speed of the car. In this case you would make your shutter speed a little slower, but if you wanted to have all the details sharpening focus you would have to turn up your shutter speed to a much faster number. Let’s take another example. I have photographed aircraft before and I know that in order to freeze the blades of a helicopter you have to shoot at the round 1/200th of a second or faster in order to freeze the blades of a helicopter. If you were to shoot that same photograph using a speed like 1/60th of a second, you would not see the blades because the blades are spinning so fast that in 160th of a second the blades of the helicopter have already done one full spin at least.
This is why you need to take the shutter speed into account when shooting any photograph. You might be thinking that just because you’re photographing people that you don’t need to worry about the shutter speed. The truth is that even when photographing people, you will be really surprised at how much movement there is. There is a general rule that works well when trying to figure out what speed is the minimum speed you should be shooting at. Let’s say you are using a 50mm lens to shoot some portraits. In this case you would need to make sure that your shutter speed was at least 1/50th of a second. if you were using a 200mm lens you would make sure that your shutter speed was at least 1/200th of a second. This is a general rule that works well but remember that it’s only a rule and you may have to change the numbers according to what you need to photograph. Also try to remember that this is giving you the minimum shutter speed number and it is always better to go higher than that if there is enough light and you can do so. You don’t have to follow this rule though. You can use the shutter speed artistically to create motion blur on purpose. If you’ve seen those night scenes where you see light trails caused by traffic, those photographs, are created by having an extremely long shutter speed, often in minutes to record action and movement for an extended period of time. Another example of having really long shutter speeds is astrophotography. It is not uncommon to have exposures of 20 seconds of more in order to record in a flight for something like The Milky Way. Ultimately you need to set the shutter speed to whatever suits you requirements.
In the final article we will discuss how you bring ISO, aperture and the shutter speed together to form the exposure triangle to get the photograph that you are after.