Quote Originally Posted by esearing
I think I understand...

If Hellen had taken an actual picture of a gray card with the incident meter reading and the sun behind her the gray card would appear on zone v. Bright spots and shadows fall where they may.
Agreed. An incident reading ignores the reflectivity of the objects in the scene, thus rendering them in their "true tonality" - assuming the film or media has sufficient range.

Quote Originally Posted by esearing
If Hellen had taken the picture of the grey card with the spot meter reading, Wouldn't she have had to open up 3-5 stops to get the bright spot white and the grey card on zone V? Or do you use the long exposure and reduce development dramatically to get it all on a wide lattitude film. I don't see this working at all for color slides.

Thus there is really 2 or less real stops to create the same middle grey exposure. It might have been useful to take a reflected spot reading of a grey card from the camera position to determine the variances between the reflected sunlight on the grey card and the bright wet pavement.
I don't know that we can actually determine this. I'm not clear whether Helen's spot reading was of a maximum-black area of the wet pavement, or of a reflective highlight area. That makes a huge difference in how one would interpret the reading. If the spot reading was of a highlight in which detail was to be retained, one might open up 2-3 stops, for example. If of a black area, the adjustment would be in the opposite direction - closing down 3-4 stops, perhaps.

The key point to remember is that a reflective reading gives the exposure needed to render the area being read as a middle gray (e.g. Zone V). Assuming you know accurately what area is being measured (as you would with a spot meter), you can then adjust the suggested exposure to "place" that value where it should be (or, where you want it), and everything else falls wherever it will accordingly. With B&W films (some responding better than others), you can adjust development to either expand or contract the contrast range for the desired effect. Naturally, that's not really possible with color film. The BTZS and Zone System methods are simply two different approaches to metering and development to achieve the desired result.