Cybershot T9 can be shot at up to ISO 640 (an advantage over most of its rivals) Higher the ISO, less the light is needed to get a picture. Therefore it is suitable for taking pics in setting where the available light is insufficient like for example not so well lit indoors settings, night shots etc. Typically most Point-n-Shoot(PnS) cameras come with ISO sensitivity of ISO 400. Here is a table that shows how ISO sensitivity works with any camera( both digital and film): At ISO 1600 you need only half as much light as at ISO 800 to get a picture. At ISO 800 you need only half as much light as at ISO 400 At ISO 400 you need only half as much light as at ISO 200 At ISO 200 you need only half as much light as at ISO 100 At ISO 100 you need only half as much light as at ISO 50 And so on.