ISO - What is it?

For anyone who is new to photography you will hear and read about something named ISO. What is it?
Originally it was to do with film and the terminology was used to describe the capability of the film to absorb light. Generally the lower the number, the longer the film took to absorb the light. The higher the number, the quicker it would take to absorb light.
In digital photography the basics are the same, although it now describes the sensitivity of the capture cells that form the picture in your digital image.

What has this to do with taking pictures?
It is noticeable most often when you are taking pictures with a flash, or in poor lighting conditions and you have the camera set to auto. You may take pictures and they are blurred (yes there are other factors in play here other than ISO) but the camera knows that to get a decent image on a low ISO setting, that it has to expose the capture cells for a specified length of time. Unfortunately the human hand may not keep still for that same amount of time , or the subject could be moving too, and because the length of exposure is needed to get enough light to make an image, the blurring will occur.
Most automatic camera settings will know this and try and step up the ISO setting (i.e. the higher the ISO number the quicker the exposure can be and less chance for external forces like movement to affect the image), BUT this does come at a cost.

The cost is in the quality of the image - The lower the ISO , the finer and more detailed image will be, The higher the ISO, the grainier and less detailed the image will exhibit.

The general rule of thumb is that the darker the lighting, the higher the ISO. (Of course there are always exceptions, but for anyone new this is an important fact to know)
It is one of the 3 essential items to know about basic photography together with Aperture and Shutter Speed, when you start to venture off the AUTO settings.

http://phototrek.446photography.com/2009/06/29/tips- and-tricks-exposure-part-iii-iso-settings.aspx

The resource that is provided here is a good update about ISO as, I know about this then it is a disc image of an optical disc in a format.

Also, ISO image files typically have a an extension of .iso, typically, This format is supported by many software vendors.


Thanks!