December 1, 2011
Having looked at the concept of aperture and depth of field, the next crucial function to understand in the operation of a camera is shutter speed. As the name suggests, shutter speed is the measure of the time the shutter is open when taking a photograph.
The aperture controls the flow and intensity of the light through the lens. The length of time the shutter stays open controls how long the light hits the sensor or film to create an appropriate exposure.
The fireworks explode and the glowing particles move outward rapidly. This is a fairly long exposure at 1 second; it shows the distance the particles moved during the exposure. The camera was on a tripod to hold it still.
The shutter is a very thin, light-tight curtain in the camera body that sits between the lens and the sensor or film. When the camera is fired, the shutter stays open for a measure of time that is set with the shutter speed dial. The speed settings of the shutter are straightforward to understand as they are expressed in seconds or fractions/parts of a second. Generally the preset speeds range from 30 seconds right up to 1/8000th of a second. When on “bulb” setting the shutter can be kept open manually for any length of time you choose. This would be useful for shooting night skies or in very low light conditions.
As always with photography, there are a myriad of possible treatments for every situation, so remember none of the information in these basic tutorials is definitive. There is always an exception to the rule. Your job is to find the exceptions that work for you!
To make an appropriate decision for shutter speed a few things need to be considered. How still is the camera? Is the subject moving, and if so, how fast? Do I want to show a moving subject frozen still or as a blur?
Images taken at less than 1/125th of a second can easily suffer from camera shake (a blurred image because of camera movement during the exposure) unless the camera is either on a tripod or held very still. Images taken at speeds longer than a 1/30th of a second will almost always need a tripod or monopod. You can brace yourself against a wall or a tree as well. Think laterally and use what ever is available to you.
Lets look at the ideas around freezing motion. If it’s important to capture sharp detail the shutter needs to be opening and closing faster than the movement of the subject. The faster the subject, the faster the shutter speeds will need to be. Getting a sharp image of someone walking may work at 1/125th where as the speeds needed to shoot a racing car or to freeze a ball in a tennis serve will be upward of 1/1000th of a second.
This image was taken at about 1/500th. The shot was set up and I was able to call when the ball was thrown.
Blur’s Greatest hits
To achieve a controlled blurring of motion in a photograph will take some experimentation. This is one of the huge benefits of digital cameras as you get to see the results and adjust to suit your vision on the spot. As an example, let’s say we are shooting the inside of a building. Set up the camera on a tripod and with a deep depth of field (small aperture) to take a relatively long exposure of ½ a second. The camera is in a fixed position and the subject is static so all going well our photograph would be sharply in focus. So, what if whilst we were taking a ½ a second exposure you got someone to walk through the shot? In a ½ a second they could take a good stride. The photo would still show the inside of the building in sharp detail because the camera and the building are still. It would also show a blur across the image starting where the person was when the shutter opened and finishing at the point they reached when the shutter closed. To show more detail in the moving person you can open the aperture slightly, which in turn will allow you to speed up the shutter or get the person to move slower through the frame. This long exposure of a moving subject is how that “cotton wool” effect is achieved when shooting the movement of water over a waterfall.
This image was taken at about a 1/8th of a second. I shot the same set up a few times until I had the blur just right.
I should mention briefly that the camera’s ISO function is the control of the light sensitivity of the sensor. It’s the same as ASA/film speeds, which is its measure of sensitivity or speed of film. As you increase light sensitivity there is an increase in the pixellation/noise in digital or grain in film. At really high ISO an image will lose some of its smooth tonal gradations and some detail becomes pixelated. This is particularly obvious when images are enlarged. Remember that aperture dictates shutter speeds and vice versa. If you change the ISO of the camera to a faster setting or use faster film you can maintain small apertures and get faster shutter speeds.
50 – 200 ISO = fine detail
400 – 800 ISO = fair detail, faster shutter speeds
1600 – 6400 ISO = compromised detail, very fast shutter speeds
This exposure was 1.5 seconds which gives the water a look of cotton wool. A tripod is essential for this type of work.
The thing to remember is that there is no one perfect setting for all photography, there are a series of choices or options for different situations. Working out which camera functions you need to take the images you want is the mission. It is not necessary to know every aspect of a modern camera, only the relevant bits. Fashion photographers, architectural photographers, sports photographers and landscape photographers can all use the same camera body. It is a very versatile tool, created to provide options across the board and as a result there are many different ways to use it effectively.
Photography is such a vast field that it takes years to refine your skill base. Hopefully this “Simplest Explanation” series will help to demystify the inner workings of the camera. Fundamentally if you have a good understanding of the relationship between shutter speed and aperture you are more than halfway towards a good working knowledge of the basics.
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Images and text © Andy Rasheed 2011
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