Digital ISO

I recently began editing my first week of digital photo after a trip to Key Largo. I used a Olympus C-8080, Olympus housing, Heinrichs adaptor, and Nikonos 105 strobe. I shot in 4 manual mode setups based on forum inputs and some auto modes later in the week and reduced the strobe settings as the week progressed. While I was reasonably happy with many of the photos some of the wide angle shots on the wrecks in low light were quite dark. I always had the ISO setting at 100. Should I use a higher ISO setting for this type shot? As a chemists, film ISO makes sense to me since the chemicals are changed but I don't understand what a digital camera does when the ISO setting is changed. Can someone explain how a digital camera responds when the ISO setting is changed? Thanks,

The simplest implemetation is just an amplifier. 2x gain gives one stop higher ISO.

Almost all of the cameras also change the JPEG rendering at high ISO. Some will even apply noise reduction to the raw files.

In a journeymen's sense, it increases the sensitivity of the sensor to light. While this does help in low light it also increases noise levels in the photo. At depth, on a wreck, you'd probably want the ISO set as high as possible. I'd first do some homework shots with different ISO's and find out where your camera goes from acceptable to very noisy.

Gary

When I shot with the Oly 5050, I never took it off ISO 64 because of noise. The F/2 lens came in handy a couple of times.

San Francisco Maru, Truk Lagoon ~170 ft depth