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On the basics page we covered the fact that the term ISO or ASA was a hold over from the film days. Also lower ISO number required more light than higher numbers. The trade off to light sensitivity was photo quality or grainy pictures. In the dark days of film photography, you loaded up a 24 frame roll of film with a ISO rating and shot that roll. There was no changing ISO settings. With digital cameras, we can have a new ISO setting for every picture. We also get more than 24 pictures on a roll!
While some artistic photographers will use the high ISO sensitivities to create
intentionally grainy pictures, most of us adjust the ISO numbers to ensure our picture turns out bright enough. The sample here shows a very low ISO setting on the left will allow the camera to see the bright filament of a light bulb. (And all the dust... Maid service?) You may need to click on the picture for a full size view. The image on the right was shot with all the lights off and the ISO setting at 3200. If you look closely you can see the grainy texture to the picture.
Most consumer priced cameras will have ISO numbers lower than 200 and higher than 3200. You may see L1 or H2 on the very low and high ends of your ISO selections. These are generally artificially compensated ISO settings. These are beyond the sensitivity of your camera, but through the magic of electronics, the camera will fake ISO 100 or 6400 for you.
Each camera is different for selecting your ISO rating. Most often you will be adjusting exposure and aperture first, so you may need to use the menus to change ISO. Use the ISO adjustments to compensate for the limitations of exposure and aperture.
Set your camera to ISO 200 for:
Most daytime outdoor pictures. Here you generally have plenty of light and can achieve less grainy pictures with a low ISO.
When you are taking that water picture on a bright day with a shallow depth of field and a long shutter time. This will help prevent over exposing the picture (white out).
Set your camera to ISO 1600 for:
A wedding. We all want to capture the moment at weddings. Turn off your flash. Let the professional use the flash, and everyone else try not to. It distracts the wedding party, detracts from wedding videos, and can play havoc with the professionals elaborate flash set up. (The elaborate flash set up that the bride and groom payed lots of money to have there.) Turn your sensitivity up, you can still use quick shutter speeds and reasonable apertures .
Babies. We have heard the complaint about never use a flash on a young baby, it can hurt their eyes. I am not a doctor, but I know I don't like a whole bunch of flashes in my eyes. We all want lots of baby pictures, adjust the ISO up so you don't need the flash.
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