This has been discussed in a recent filter thread and in a prior thread. Last week I was experimenting with a Kodak Wratten ND 4.00 100cmx100cm filter. The ND4 gives 13 1/3 stops of negative exposure value. My D2x apparently meters through the prism, not the lens, so I underexposed this first real test shot by a stop and a half or so guestimating the bulb setting (around 30 secs.) Therefore, I had to set a black and white point in Capture NX to bring it back to spec- I'm not sure if that or the ND filter are responsible for the Kodachrome look, more detailed testing will figure that out in the future. There was traffic on the highway, additionally, I circumnavigated the camera while counting out the seconds, passing in front of the lens once. I'm fairly confident that this lens will allow me to get most people out of a crowded scene for a project I want to do.