SOME INTERESTING OBSERVATIONS REGARDING THE NATURA BLACK:
As you may know, when ISO 1600 or higher film is loaded in the camera, the camera goes into NP mode, which permanently suppressed flash usage, limits the long exposure time to 1/45 of a second, disables +/- 2 stop manual exposure compensation, and kicks in a programmed automatic exposure program that provides some degree of overexposure (I think up to 3EV depending on light level). This is designed for well-exposed photos in low light, hand held with no flash.
BUT WHAT ANNOYED ME ABOUT NP MODE is the lack of shutter speeds longer than 1/45th, as well as the ability to manually set exposure compensation (up to +/- 2 stops).
SO, I recently took a roll of Fuji Natura 1600 film and re-DX coded it to 800 (took 3 minutes, really easy to do). Then my Natura Black was NOT in NP mode, plus I prefer to overexpose Natura 1600 film anyway, especially in incadescent light conditions. I then had logn shutter speeds, and exposure compensation, BUT THE PRICE TO PAY is the need to manually turn the flash off each time the camera is powered up (if you don't want flash, and I usually don't). That is a bit of hassle, but you get quick at it with the button pushing.
The results from this roll at ISO 800 were better exposed than the 1600 results I was getting in NP mode (subject was dimly lit party - so primo Natura Black territory).
BUT HERE'S THE REALLY INTERESTING BIT: I tried an experiment (only one frame) in which I covered the flash with a piece of black tape and DID NOT DISABLE THE FLASH - the frame came out perfectly exposed, leading me to hypothesize that when using flash, the camera attempts to balance ambient and flash exposure to some extent, and therefore if the flash is absent (or weak) the shutter stays open longer to compensate.
This observation needs to be investigated further.
If this is true, then several possibilities open up: permanent tape over the flash for those times when you need to grab a quick shot without flash and don't have time to do the button pushing excercise (or forget to) disable the flash, as well as putting a ND gel filter over the flash to custom balance flash and ambient mix.
Like I said, somebody (maybe me) needs to play with this more.
The Natura Black is definately and interesting camera!