Last year, I was in Death Valley, trying to take photos of patterns in the sand. I've got one of those newer Minolta Flashmeter VIs that can do both incident and reflected measurements. I used the spot meter while there and some of the scenes were only about 3-4 stops (reflected) between the darker and lighter portions of the scene. Using Acros and Xtol, I was able to develop the film enough to expand it out to where it prints well.
Today, I was flipping through my copy of the BTZS book (3rd Ed.), and I thought back to the Death Valley stuff. So I was looking for a description of how to meter scenes of low contrast using BZTS. Using an incident meter, it looks to me that the BZTS system can't measure scenes that have SBR's less than 5. It also seems that it can't differentiate between a 5 SBR scene and a 3 or 4 SBR scene.
I know you can determine development times for SBR ranges this low, but how do you actually measure them with and incident meter. Does photographer's discretion (i.e. override meter readings) kick in here?