I will talk much more about the high ISO capabilities of the D3 when addressing wide angle. However, while shooting macro I was not creatively inspired by this ability and shot almost entirely on base ISO 200. On a couple of occasions I tried using ISO 800 to shoot balanced light macro, but found this quite a hassle. First you have to adjust ISO, then shutter speed and then flash power. With cold hands, in the chilly waters of British Columbia, my enthusiasm quickly waned for this technique. If this is a technique that appeals I would recommend ensuring you have TTL strobes, it is one less thing to adjust. Or don’t even bother changing the ISO and just slow the shutter speed down 3 or 4 stops and concentrate on holding the camera steady!
Perhaps the most common argument in favour of 12MP FX sensor over a 12MP DX sensor for macro underwater photography is diffraction at smaller apertures. In studio tests its possible to show that the more densely spaced the photosites on a sensor the more diffraction will occur reducing the detail captured at smaller apertures. While I do not doubt diffraction occurs in our underwater photos, I feel that in the real world there is so much else going on that influences sharpness (not least of which is shooting through murky seawater) that it is not such a limiting factor. When I shoot my DX underwater camera I do not see any significant reduction in sharpness between F11 and F22 (or more) – I just see more depth of field. And neither when I shot the D3 did I suddenly find that shots taken at F16, F22 or more were sharper than I had seen on DX at the same apertures. In respect of diffraction I did not find any practical advantage for using FX for macro on real subjects. I don’t believe that this is a factor that underwater photographers should be overly concerned with.
That said the D3 produced excellent image quality for macro. The pictures looked great on the LCD and even better on my Mac. I was actually surprised when I pulled up some D2X pictures and started examining them at 100% that there was not much to choose between the 12MP RAW files from each camera. The D3’s LCD had me convinced it was a step on in image quality!
In conclusion I found the D3 a fine camera for macro shooting once I had selected the appropriate lens for the appropriate subject. I didn’t feel that if offered any obvious advantages over a DX camera, but I was also pleased to discover it was not inferior in any way. Nikon’s new high-resolution 3 inch LCD is exceptional (and also found on the D300, D700 and D90) and leaves you in no doubt that you have nailed the focus and exposure.