When talking about Exposure, Aperture and the Shutter Speed are two features that actually control the amount of light that hits the sensor or the film (Sensor Speed does not actually control the amount of light). Here, let us discuss Shutter Speed and its effects on the photograph.
Before coming to shutter speed, first let’s take a look at the shutter itself. The shutter is a gate that blocks the light rays hitting the sensor. Its duty is to open up when required (when the ‘shutter button’ is pressed) and let the light rays to travel towards the sensor to expose it for a specific period. The sensor or the film has to record the image within that period.
There were numerous types of shutters along with history. The very first shutter was the mere lens cap. Then the photographer had to open the lens cap, wait for some time, and close the cap again himself. Today there are even electronic shutters which do not have any physically moving parts. I am not going to talk about the history of shutter in detail since this article would be extensively long if I do so.
Types of Shutters
All the shutters in history can be grouped into two main categories, according to their placement, namely, Leaf Shutters and Focal Plane Shutters.
Leaf Shutter : The shutter is placed within the lens assembly, among the lenses, in front of the lenses or after the lenses.
Focal Plane Shutter : The shutter is placed right in front of the image sensor (or film).
Leaf shutters have gone obsolete and cannot be found in new cameras. All the cameras nowadays have focal plane shutters. As of today, there are three types of focal plane shutters, according to their way of exposing the sensor. They are namely, Mechanical Shutter, Electronic Shutter and Electronic Front-Curtain Shutter.
Mechanical Shutter : This is the most common type of shutters in today’s cameras. They are made of two metal curtains that move vertically (earlier once had horizontally moving curtains also). One curtain is covering the sensor when the camera is standby. Once the ‘shutter button’ is pressed, that curtain moves out letting the sensor to be exposed. After the given time, the other curtain moves in to cover the sensor again.
Electronic Shutter : In this type of shutters, there are no moving parts that cover-up and expose the sensor. It all happen within the sensor. In simple terms, they work by turning on and turning off the sensor for the required period. These shutters are found in Mirrorless Cameras and still not very popular.
Electronic Front-Curtain Shutter : In this type, a combination of the mechanical shutter and the electronic shutter is used. It is called Hybrid Shutter for the same reason. What happens here is, exposure is started electronically by turning on the sensor and stopped mechanically by closing the curtain.
The period of time when the sensor is exposed is decided by the speed of shutter blades opening up and closing down. And it has to be instructed by the photographer or the camera itself will select an optimum speed when it is in auto-modes. The amount of time the shutter takes to open up and close down is defined as the Shutter Speed. It is the time that the gate remains open. In other words, it means the amount of time the sensor (or film) is exposed to light. The term ‘exposure time’ refers to the same meaning.
When the shutter is open longer, we generally call it ‘slow shutter speed’ (because the shutter blades are slow in opening and closing) and when the shutter is open for a shorter period, we call it ‘fast shutter speed’
How to Measure?
Shutter speed is measured in seconds. In fact, almost all the times, a shutter speed would be a fraction of a second (ex. 1/60 s, 1/125 s). There are scenarios where we have to use shutter speeds slower than even 1s. We will come to that later.
The standard series of shutter speeds would be like,
1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s etc
But in most modern DSLR cameras, there are numbers of intermediate shutter speeds plus several slower and faster shutter speeds than the above mentioned series. As an example, my Nikon D7200 has 55 shutter speeds starting from 30s to 1/8000s.
There is another shutter speed called ‘Bulb’ in almost all DSLRs today. It doesn’t have a specific time assigned to it. Rather, the shutter remains open until you press and hold the shutter button. The shutter is closed once you let go the shutter button. This will be highly helpful for creative and artistic photographs which you may not decide the required exposure time beforehand.
In the practical world, most of the time, photographers don’t express shutter speeds as 1/60s or 1/250s. Instead, they are expressed as 60 or 250. So, if you are ever told about a shutter speed 125, then you should know that it means 1/125s.
Shutter Speed vs Exposure
I guess you can clearly understand the relationship between shutter speed and exposure. If the shutter speed is slow, more light is allowed to hit the sensor, hence it will give a higher exposure. On the other hand, when the it is high, less light is permitted to hit the sensor. Therefore, it will give a lower exposure. In other words, exposure will be increased when the ‘amount of time that the shutter is open’ is increased (when shutter speed getting slower).
To make things even more clear, let us do a little demonstration. Let us shoot the same object with different shutter speeds and see how the exposure would be. All the photographs are taken with constant f-number and sensor speed, f/2.2, and ISO 125.
First one is the photograph with correct exposure.
For f/2.2 and ISO 125, the camera gave 1/320s as the correct shutter speed to maintain the correct exposure. Now let’s change it manually.
It is clearly visible here, how the exposure going under when the shutter speed is increased. Now let’s make it slower than 1/320s.
On the other way, exposure begins to go over when the shutter speed is decreased.
Side Effects of Shutter Speed
Shutter speed is also used as much as the aperture, to control the exposure. Reducing exposure can be done with the shutter speed without any issue, by increasing the speed. But you don’t get much liberty in increasing exposure with shutter, as much as you get with aperture. Because, when you are lowering the shutter speed to increase exposure, at a point, ‘Motion Blur’ begin to be introduced to the image.
Motion blur is the apparent streaking of moving objects in a photograph.Wikipedia
Motion Blur can occur when a moving object gets recorded on more than one place in the frame, due to its motion. To get a sharp still image, the object(s) should be in the same place in the frame while the shutter is open. But if the object(s) moves while the shutter is open, that motion will be captured. Not only the movement of the object, but also jerks in photographer’s hand may bring motion blur.
Let us do another demonstration to witness this. (For this I have to borrow my two-months-old son’s toy Merry Go Round.:)) I made it spin and shot it in various shutter speeds.
You can see that when shutter speed comes to 1/1250s, ever part of the toy is sharp and frozen. (Don’t be misled with the out-of-focus red cones in the front and back. It is not the motion blur, it is the effect of depth-of-field.)
‘Unintended’ motion blur may ruin the photograph almost all the time. Why did I mention the word ‘unintended’? Is there intended motion blur? Of course, motion blur is added to photographs intentionally some time. Let’s get into that later.
Getting Rid of Motion Blur
If moving objects are photographed, fast shutter speeds have to be selected in order to avoid motion blur. Shutter speed depends on the speed of the object. You will need an extensively fast shutter speed to capture running car frozen, than to capture a walking man. So if you are capturing a fast-moving object, you have to select a higher speed and adjust the exposure by other two, aperture and sensor speed.
When talking about motion blur occurs by the jerks in hand, if the shutter speed is fast, we don’t have to worry about it very much. But when we have to make it slower to increase the exposure, there will be a risk of having blurry images. Normally, it is a common belief that with 50mm lens, the slowest shutter speed we can go with hand-holding the camera is 1/60s, given that the object is not moving.
And when the focal length increases, the effect of a jerk is getting higher and higher. I guess you could understand that a tiny movement in the camera can result in a massive deviation of the frame when the focal length is high. Therefore, 1/60s will not be a good shutter speed for a shot with a 300mm focal length. To get rid of the motion blur caused by the jerks of hand, a tripod or at least a mono pod has to be used. That way, you only have to worry about the movement of the object.
Photographers use tripods often when they take night shots low light shots. They tend to slow the shutter speed to get the exposure correct in the low light conditions. By using the tripod, they can avoid worrying about jerks of hand.
An image like this may require a very slow shutter speed to bring the correct exposure, probably slower than 1s.
Intended Motion Blur
Motion blur may be introduced to an image intentionally to highlight speed/ movement of the subject or to add an artistic touch to it. As an example see below images.
These photographs show the speed or the movement of the subject. Imagine if they were captured at high shutter speeds freezing the moment. Then they will not bring the sensation of speed or movement just like these do.
Now take a look at these images.
Capturing at slow shutter speeds have brought an expressive artistic value to the above images. These photographs would have become ordinary images if they were shot at higher speeds without any motion blur.
So I guess you have got the point now. Motion blur can be used to create stunning, expressive and artistic photographs, if used correctly.
To sum up the discussion, Shutter Speed is one of two features that control the amount of light hits the sensor, in other words, exposure. By slowing down the shutter speed, exposure is increased and by increasing it up, exposure will be decreased.
Motion blur is the effect of recording the movement of the subject in the photograph. Usually, it would ruin the image, but not necessarily. If used carefully, motion blur can add an expressive value to the photograph. To get rid of motion blur higher shutter speeds are required.