I have a Nikon D7000 camera that had a supercolor conversion done by Life Pixel.. Supercolor means that it will pass wavelengths greater than 590 nm. I am becoming more interested in black and white and heard that a conversion to 830 nm gives more contrasty images. I was sorry that I had the 590 nm conversion until I realized I could use an external 830 nm filter. When this filter is being used, since it is virtually black, you can't see through the viewfinder. it's as if I'm using an ND filter. However I can see in live view in order to focus and compose.
As when doing a long exposure I needed to determine the correct exposure time. So I set a base exposure of iso 100, f16, 1/250 seconds and then took a bracketed set of images to determine how many stops I would have to increase the exposure by to get a histogram that was exposed to the right.. This happened at 1/8th of a second which is approximately 5 stops.
I repeated the experiment with a 720 nm filter. The result was about 4 stops (1/20 sec).