ISO Speed Explained

Your camera's ISO speed is a measure of how sensitive the sensor is to light. If you remember using film you probably bought 100 speed or 200 or 400 speed film. The higher the number the 'faster' the film and people often thought this meant you could use fast speeds to photograph fast things like cars. Well that's partially right. ISO speed actually refers to how quickly the camera reacts to light and records an image. A low speed works great when there's lots of light and a high speed works better when it's a bit dull or dark. So why would you need to change ISO speed if you can alter exposure using shutters and apertures? Well sometimes there just isn't enough light to use a fast enough shutter so you can change the iso. The downside is a higher ISO gives you more sensitivity but at the cost of image quality. there's more on using ISO speeds on our site at http://www.photographycourses.biz/using_iso_speed.html.