Reiterating the Exposure Triangle, there are three parameters that can be adjusted for varying exposure in a photograph. The areas are:
- ISO
- Aperture
- Shutter speed.
What is Shutter Speed?
Wiki defines Shutter speed as a common term used to discuss exposure time, i.e. the effective length of time a shutter is open.
In digital cameras the Shutter speed is the length of time the shutter is opened, allowing the image sensor to be exposed to the light source and thus the image you're attempting to capture.
Shutter speed is always measured in seconds and fractions of seconds. You often see Shutter speed indicated by 1/60 or similar values. This simply means that the shutter is opened for 1/60th of a second. Shutter speed of 1/250 is faster as compared to 1/60.
Most cameras and photographers can reliably take photos in speeds of 1/30th of a second or better. However most modern Digital Cameras now have image stabilization functions (Canon's IS or Nikon's VR) that allows the even lower shutter speed to be used without the assistance of a tripod. Without this image stabilization you would almost always see a 'camera shake' in your shots. A camera shake occurs when the camera 'moves' when the shutter is opened (shutter button is pressed) and would result in blurred images. A DSLR when held by hand will have its shake even for professional photographers. That is why devices such as tripods and gorilla pods are used to eliminate camera shakes.
Almost all cameras have shutter speed that doubles each preceding value. As an example you have 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500 and so on. Now why is this so you may ask... The main reason to this is simply that aperture settings also double up the amount of light that is allowed to come in when you open it wider. When you increase the shutter speed by one stop (faster) and decreasing aperture by one stop (wider), the camera would yield similar exposure level.
Apart from fractions of a second, most cameras will also give slower shutter speeds in seconds (i.e. 1 second and slower). These settings are often used in special scene photography such as night photography or star photography. This settings will definitely require the use of a tripod device to stabilize the camera. Some cameras also provide the B Shutter Speed. 'B' stands for Bulb mode where the camera will keep the shutter opened as long as the shutter button is pressed (and not released).
There is no fast rule on what shutter speed that you need to use in shooting a photo. If you're taking action-mode photography such as football matches, you definitely would want to have a higher shutter speed to freeze the movement and eliminate blurry images. You can also reduce the shutter speed to obtain a slightly blur image to capture the sense of movement.
One key point to keep in mind is that the focal length of the shot. The longer the focal length of the shot (i.e. when using zoom lens) the higher the chances of camera shake to occur. This can be compensated with a higher shutter speed. So to get the same exposure in a 50mm focal length shot of 1/60th Shutter speed you may need to use 1/125 shutter speed at a focal length of 105mm.
If you have used zoom lens you may notice that the lens may have 18mm-105mm and the numbers 1:3.5-5.6G ED (Nikon 18-105mm lens). the number 3.5 means the lowest (widest) aperture setting at 18mm focal length and the number 5.6 means the widest attainable aperture setting at 105mm focal length. I'll cover the G and ED in other postings later. This is a point to remember that zoom lens typically have lower range of f-stops. This effects the Depth of Field capabilities of the image that you want to shoot at longer focal lengths.
On a final note, remember that if you reduce the shutter speed one stop (i.e. 1/125 to 1/60) for a given shot, you will need to reduce (widen) the aperture settings by one stop (i.e. f16 - f8) to get the same exposure. If you have grasped the understanding on the Exposure Triangle and the relationships of the three (ISO, Shutter speed and Aperture), you will also find that you can also lower the ISO rating to achieve the same effect.
I have some examples on shutter speed differences of the same object. The first two was shot on a focal length of 55mm (DX) and the second pair was shot on a focal length of 135mm (DX).
Focal Length: 55mm (DX)
Shutter Speed: 1/25
Aperture Setting: F22
ISO Setting: 400
Program Mode: Aperture Priority
EV Value: +0.33EV
Flash Not used
Focal Length: 55mm (DX)
Shutter Speed: 1/640
Aperture Setting: F4
ISO Setting: 400
Program Mode: Aperture Priority
EV Value: +0.33EV
Flash Not used
Focal Length: 135mm (DX)
Shutter Speed: 1/1250
Aperture Setting: F5
ISO Setting: 400
Program Mode: Shutter Priority
EV Value: +0.33EV
Flash Not used
Focal Length: 135mm (DX)
Shutter Speed: 1/8
Aperture Setting:F29
ISO Setting: 100
Program Mode: Shutter Priority
EV Value: +0.33EV
Flash Not used
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