Photography and movement
Why are photographers always portrayed as shouting “Hold it…” before the flash gun goes off? Like all clichés, there’s something behind it.
As explained in our page Photography and light, cameras need light to work. The light from the subject goes through the lens and into the camera, and a device inside - these days an electronic one, though in the old days it was a piece of chemical film - captures the picture. Of course, if the camera did that all the time it would be continuously capturing light, so it has a device called a shutter which blocks off the light except when you actually take the photo. When you press the button to take the photo, the shutter opens for a set amount of time, the photo is taken, and the shutter closes again. Simple. The time the shutter is open for is called the ‘exposure’ time, or ‘shutter speed’. It’s usually measured in fractions of a second. A typical exposure might be 1/100th of a second.
And as we also explained in our page Photography and light, one way to deal with situations where there is low light is to arrange for the shutter to stay open for longer. If the shutter stays open twice as long, roughly twice as much light gets into the camera. Which is fine if both the subject and the camera are perfectly still.
The trouble comes when either the subject or the camera is moving - or both. The shutter opens and a small amount of light enters the camera. Then the subject moves a bit, but the shutter is still open, so more light enters the camera but is now captured in a slightly different place. Instead of capturing a sharp image, you get a blur. The example below illustrates this:
There’s very little we can do about blurred photographs.
Firstly you should always make sure your camera is as still as possible. With normal shitter speeds, i.e. 1/100th of a second or shorter, it’s probably OK to hold the camera in your hand. For slower shutter speeds you may want to stand the camera on a table or other solid object. Better still, get a tripod - most cameras have a fitting for this.
Secondly, try to use the fastest possible shutter speed for the amount of light available. Most cameras do this automatically, but they are designed for taking photos of people and scenery. If you are taking a photo of something moving quite fast you may want to override the automatic settings (your camera’s manual will tell you how).
If you have a relatively sophisticated camera you may be able to select a higher ISO number, which, in effect, makes the camera capture more light at a faster shutter speed, but with some loss of image quality (your camera’s manual will tell you if you can do this, and if so how). If you can change the ISO number, don’t forget to change it back afterwards, or your camera will struggle to take good photos under normal conditions.
As mentioned above, cameras used to use chemical film to take photographs. It wasn’t that long ago - digital photography only really became available to ordinary users at about the beginning of this century.
When photography first started - in the 1800s - the chemical films used were not very sophisticated. They took a long time to capture the image, and so exposures had to be long. Shutter speeds in those days were measured in seconds, not fractions, and being photographed required you to hold absolutely still for, maybe, twenty seconds. So much so that photographers devised mechanical devices like clamps to hold the subject’s head still. Perhaps now you can see why the people in those early photos are rarely smiling! But it was an improvement over sitting still for about a week while an artist painted your portrait, so it caught on.
Then they invented flash and things improved a bit, but even then the subject had to remain fairly still while the photographer focussed the picture (manually), held up the tray of flash powder, manually opened the shutter, ignited the flash powder and then manually closed the shutter. Still quite a performance by modern standards.
We hope you find these tips useful. If you have any feedback or suggestions please contact us.
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