The role of shutter speed in photography – At heart, cameras are really pretty basic tools. Admittedly, they take a lot to master, but their basic functionality is not so complex. They are essentially just lightproof boxes, that we selectively let light into to expose the film or sensor. There are only three ways light comes into a camera: via the aperture, the shutter, and the ISO. Today I want to look at the role of the shutter speed in all this.
Shutter speed controls two things in photography. One is the duration of time that light is entering the camera. This is achieved in most cameras by the use of a focal-plane shutter. There are other types of shutters, such as leaf shutters and electronic shutters, but that’s for another day.. The focal-plane shutter common in digital cameras contains two shutter curtains that travel down right in front of the focal plane (hence the name) and control how long the sensor is exposed the light. The first shutter comes down, letting light in, and the second one comes down behind the first at the chosen interval of time, thereby controlling the duration of the exposure.
The second thing the shutter is responsible in photography is connected with how it works. Because the shutter is responsible for time in photography it is also entirely responsible for movement in natural light photography (flash is also capable of freezing movement very successfully). Time and movement are connected at the hip and cannot be disconnected, and so when we think about how to understand and control shutter speed, we need to realise we are controlling both time and movement with this one setting.
This Youtube video below shows the internal workings of the aperture, mirror and shutter curtains during an exposure. If you watch carefully you will see the two curtains coming down very close together, leaving a small slit travelling down the sensor. You will also see how the mirror first comes up out of the way and that the aperture only then sets itself to the chosen f stop. It’s a marvel of mechanical engineering and a really ingenious way to solve a set of problems and is the heart of how photography works.
OK, so now we can see how the shutter curtains work. So now let’s look at the two things they control, time and movement.
With photography, there are two types of movement we need to control. There is camera movement, and there is subject movement. Camera movement during an exposure creates camera blur, an unfortunate softening of the recorded image. It is also not very evident at times, as the image can look sharp on the camera screen, and it’s only when we get it home on a larger computer monitor we realise that it’s a bit soft. Many shots are ruined by this, and it is easily solved by paying close attention to the shutter speed (although that’s harder than it sounds). Obviously if we place the camera on a tripod, camera movement is taken out of the equation (as long as it’s a decent tripod and it’s not really windy), But for hand held photography, we need to consider the shutter speed with every image we take.
There is no hard and fast rule as to what shutter speed you need to use to avoid camera movement during an exposure, as it depends on both the photographer’s stability (their pose, their grip, and even their breathing can play a part here) and the focal length of the lens they are shooting with at the time. Huh?? Focal length of the lens? Why does that have anything to do with it? Well, imagine a camera that is zoomed right in on something. A small movement of the camera and the subject moves a lot in the viewfinder, right? Now imagine a very wide angle lens. The same amount of camera movement does not affect the subject’s position anywhere near as much. So we can see that movement is magnified, so to speak, with longer focal lengths, and therefore the longer the focal length, the faster the shutter speed we need to ensure movement is not being recorded during the exposure.
There is a guide for this, to simplify matters. The guide says that to reduce the chances of camera blur in handheld photography:
the shutter speed should be = or > than the inverse of the focal length.
This means simply that if we are shooting with a 50mm lens, our shutter speed should be at least 1/50th of a second to avoid camera movement. If we changed for example to a 200mm lens, we should increase our shutter speed to at least 1/200th of a second. If we shoot with a really wide angle lens, like a 24mm, we could perhaps get away with a 30th of a second. Some photographers can shoot hand held at ridiculously slow shutter speeds, like 1/15th or 1/10the of a second, but to play it safe keep the guide in mind. This approach will minimise cameras shake. Just remember, if you have plenty of light and can choose a faster shutter speed, you can safely do so. The guide is the minimum speed you need to control camera movement, and it sure doesn’t hurt to use a faster one if you can. To read more about camera shake, read this previous post on my blog.
Then we have subject movement. It’s a completely different kind of movement. Even if we are on a tripod, and can avoid camera shake with long exposures, that won’t help us if our subject is moving. It’s ok for buildings and rocks and other static objects, but anything for that moves, we have to consider their movement. If for example we want a crisp, sharp shot of a person walking, we might use a shutter speed of 1/125th or faster. If our subject was a car we might need 1/500th or faster. If it’s a fast car, we might need 1/2000th or more. If we are trying to freeze something extremely quick we might need to go all the way to 1/8000th of a second. These are not hard and fast figures. Again, it’s just a guide, an idea of where to start and how to think. Trial and error will determine the correct shutter speeds, but again, remember that if you have the available light, and you are trying to freeze movement, then using a faster shutter speed than necessary will only help.
Image Stabilisation (Vibration Reduction)
IS or VR (or whatever the other manufacturers call it) is all the same thing. Sony put it in their bodies, but Nikon and Canon put it in the lenses (presumably so they can sell more of them). If you have an IS/VR lens, then the first thing to know is not to just leave it on all the time. It’s not meant to be used whilst on a tripod and it can actually have the opposite effect in such conditions, but apart from that, it also uses more batteries. So the way I use it is simply to turn it on when I need it.
This is how it works. You know what a stop is right? If not, you need to come to one of my Beginner Classes. But in any case, turning IS on gives a photographer 2 stops (the manufacturers often claim 3, but in the real world, 2 seems to be more realistic) of leeway when considering that rule about hand held photography. So if before we were using a 100mm lens and needed to be shooting at 1/100th of a second, turning IS on will allow us to go to 1/25th (two stops slower) of a second and still avoid camera shake. It’s amazing technology, and it makes for a very useful tool in low light. but remember, don’t just turn it on and forget about it. Use it when you need it.
Panning is a technique where we use slow shutter speeds to start to deliberately record movement (wouldn’t want IS on here), but where we pan the camera in sync with the subject to keep the subject sharp. It is a difficult technique to master, and you might shoot 20 frames and only get one or two that are sharp. But it’s a great way to portray movement, as it’s so dynamic. Great for triathlons, or bike races, or even just kids on skateboards or skates.
Obviously, with all images we are dealing with time. But let’s look at what the camera can do with longer exposures, when we are not trying to freeze objects but rather allow for movement in the exposure. With these shots we need to carefully control movement, both camera movement and considering subject movement. The area of long exposures is one of the greatest creative areas in photography in my mind, but it is a difficult skill to master as there are a lot of variables and it can often be more trial and error than precise calculation.
If we were shooting a long exposure of a building and the camera was on a tripod, then the chances are we will not be recording any movement at all, unless the sky is full of racing clouds, or there is other movement in the foreground. A still camera and a still subject will give us the same visual result as a fast shutter speed shot.
But if we are taking a shot of the waves by a river or the ocean, then the result will be vastly different. The rocks and other non moving elements will be sharp and clear, while the water (depending on how long the exposure is and how much movement there is in the water itself) will blend and merge and take on a misty appearance from all the recorded movement. There are any number of applications with a tripod, a long exposure and a moving subject. Think of those milky waterfall shots. Or light painting, a favourite of mine. Or just beautiful landscapes with moving clouds and silky water… The possibilities are endless. You just have to pick your subject well. People, for example, are not so great a subject in long exposures. They tend to be unable to be as still as needed :)
Likewise if we are playing with lights. A google image search on painting with light, or low light photography will throw up an enormous range of possible images, but they all share the same characteristics. Any movement (the trailing of a light source for example) will show up and any elements not moving will be exposed as they would normally look. In these shots, the shutter speed does a few things. It gives us the time to “play with the lights”, and it builds the ambient light exposure. If it is dark night, then a 30 second exposure will look much the same as a two minute exposure, but just after sunset, the differences will be great. But in these situations, the aperture is also quite important. It needs to be the right size for the brightness of the light source. If the aperture is too open, the light source will burn out (turn pure white) and we will lose detail. While fraught with technical issues, painting with light is awesome fun and is very much trial and error.
One way people can be very useful in long exposures though is with a ghosting technique. This is where we have a subject being very still for a percentage of the exposure (around 1/2 to 2/3rds) and then they quickly get up and move out of the frame. This means that for the remainder of the exposure, the camera is now recording what was behind them, and this results in both subjects being recorded with an amount of transparency, giving the result of making them look quite like we’d imagine a ghost.
Flash Freezing Movement
I won’t go into too many details, as I have another blog post here about this subject, but in brief, flash is also very capable of freezing movement in low light. It’s actually much better at it than shutter speeds as the duration of flash can be extremely brief. But it needs to be in low lighting situations so ambient light doesn’t play a role in lighting the subject. With the right flash settings, you can achieve an effective exposure of 1/30,000th of a second, That will freeze just about anything short of a bullet.
Obviously, the length of the exposure has a huge impact on the type of photo you are going to get. You always have to think of the camera movement and the subject movement and make sure your chosen shutter speed will give you what you want. Long exposures open up a world of creativity, but good control of short exposures is just as important. At least one thing is very simple here. If there is an issue with movement, look no further than your shutter speed. With movement and time, it is the Boss!