While on land, I can slow down my shutter speed, increase my Apature or Bump up my ISO to increase light.

OK, Bumping up my ISO decreased quality, and Shutter speed and apature are object specific.

How does this effect my picturs underwater?

Does light mean colour?

Remember your basc scuba class: roygbiv? That is the light spectrum in water, or the order in which light dissipates due to water density. It means:

Red
Orange
Yellow
Green
Blue
Indigo
Violet

This is the order in which light is filtered out of the water column, the first three going in 15-30 feet. A cut on your finger produces green blood at 30 feet. Your ISO set to 100 or 1000 won't bring back those missing colors. You need artificial light to bring back the reds, oranges and yellows using a strobe. Deeper water means you need artificial light to bring back more missing color, such as green. You might get away with some kind of magic filter and a higher ISO, but the basis for ISO to color has little or no correlation.

Joe

The lenses and ports I use are sharpest at f 8 to f 11. I like to keep shutter speed above 1/60 to avoid motion blur. Typically I use 1/100 to 1/200 to get the water color I want and depending on the amount of ambient light. To make this work I have to use ISO 400 which is noisier than lower ISO settings, but not noticeable to me in underwater pictures or land pictures for that matter.

Details here.

http://www.splashdowndivers.com/photo_gall...gs_exposure.htm

http://www.splashdowndivers.com/photo_gall...ettings_iso.htm