what is the difference you might see in files at both a high ISO and a low ISO?

Answer 1

A high ISO will be fast and will lose detail. If you are using a digital camera the digitization will show when you blow the picture up, or enlarge it. A low ISO is slow, exposure times are long, you get a greater amount of detail, and it can be blown up, or enlarged, to a bigger size.

Answer 2

The higher the ISO you use the more chance you get of creating 'noise' in your images. On film, this happens mainly with 1600 but does show up in 800 speed also. This is caused by loss of detail due to the high speed. If you use a digital camera, this 9/10 times happens in the blue channel (often referred to as 'blue noise') and can easily be corrected in most graphic editors.

A low ISO records a better image and produces a better image when blown up beyond a 16x20 image. Low ISOs (60 - 100) are used for portraiture and fine art photography whenever there is ample light or a high amount of controlled light.

Answer 3

You will get a lot of noise in the picture. You will see several oddly colored pixels, as well as a more pixellated look to the photo overall. It is best to use the lowest ISO setting to get the best picture, but in low light, or action, your still better off with a little noise or pixellation than a blurry photo.