Arguably the most exciting photographic capability of the D3 is its noise free performance at high ISO. I was interested in investigating how useful this was beneath the waves. Underwater I found that I could shoot up to ISO 800 without any noticeable degradation in image quality. ISO 1600 could still produce excellent double page spreads and ISO 3200 would be good enough for covers or single page spreads. Incredibly impressive. Nikon users have never known anything like it. The D3 changes how you think about light.
Perhaps my biggest surprise with the D3’s high ISO performance was how I struggled to find subjects that really made use of ISO 1600 and above. On this trip I dived in some pretty dark waters. Below the kelp, in the gloomy waters of British Columbia on a (typically) rainy day is not bright. However, shooting typical wide angle scenes with flash, I found that I never needed an ISO higher than 800. Sure, I could dial in higher ISO settings and they worked, but at ISO 800 I was able to use all the aperture and shutter speed combinations I wished. In other words you have to do some pretty unusual diving to really “need” ISO 1600 to 6400. The obvious examples would be deep or dark available light shots, such as wrecks, particularly with filters.
When you use the ISO settings above 800 you do begin to degrade image quality - not much, but its visible. Therefore it is important to make sure that the ISO setting is getting you something photographically that could not be achieved at a lower ISO. Up to ISO 800 you can increase for free, above this you should not just be using ISO as a crutch for poor technique. I believe that there are many interesting and novel underwater images to come from high ISO shooting. I really felt that I only just started to make use of this potential during my shoot.