Why ISO??

[beesparkle]

Could anyone help me with an answer, I am struggling to learn and understand all this photography mularky!! and wondered why on digital cameras do we have ISO? if it was originally the ASA film speed why do we need it on digital when we have shutter speed and aperture and exposure control?

from confused!!

[nwyman]

Could anyone help me with an answer, I am struggling to learn and understand all this photography mularky!! and wondered why on digital cameras do we have ISO? if it was originally the ASA film speed why do we need it on digital when we have shutter speed and aperture and exposure control?

from confused!!
Because it is yet another variable that helps to achieve the amount of light that exposes the image sensor (this is not me talking, but a book I refer to a lot "50 Fast Digital Camera Techniques" by Gregory Georges).
While you're starting out, just set it your ISO to it's lowest setting, or Auto, and practice the other stuff. I really only mess around with ISO when I'm indoors in a low light situation and don't want to use the flash. This comes in handy in museums when flash is not permitted.
Nancy

[adas]

beesparkle, there are only three ways for adjusting the amount of recorded light in the camera: Aperture, Shutter and Sensitivity(ISO). For a given subject, reducing one of them you have to increase the other(s) and viceversa. Wich one to change is a matter of choice or photographic technique.

[Bodryn]

There is another important consideration with digital cameras. If you use higher ISO settings, a lot of "digital noise" can be introduced. These are, for example, areas of colored pixels or artifacts that bear no relation to the actual colors that should be in the photo. You can especially see this effect if you use a high ISO setting and take a picture of clear blue sky, then take another similar photo at the lowest ISO setting and compare the two photos. For best photo results, keep the ISO as low as possible given the other factors such as available light, etc.

[Jon]

ISO stands for the International Organization for Standardization (I know, but it really does), which took over the job of managing standards from the American Standards Association (ASA), British Standards Association (BSA), and Deutsche Industrie Normen (not, as some would have it, Das Ist Normall - DIN). It's a measure of how sensitive film/a sensor is to light. ISO in digital allows us to fine-tune the response of our sensor to get optimum results wiht our preferred choice of shutter speed, aperture, and sensor noise level.