Forget about 'Zones'. They're merely a (very clever) way of describing the tonal scale of a print. Shadows are shadows, whatever Zone label you care to use. You can call the darkest shadows with texture Zone 2 or 3 or ten million; what you call them is irrelevant to what you see on the print. Indeed, there have been several versions of the Zone System, from the original (I to IX, symmetrical about V) through asymmetric (add Zone X) to the long symmetric (0 to X -- quite amusing as there was no 0 in Roman numerals). This is what I mean about the Zone System being over-complicated and jargon-ridden. Look at basic sensitometry instead.
You need enough exposure on the film to give you texture in whatever area you choose. This can mean anything from letting unimportant shadows go black (useful in many kinds of theatre and music photography) to keeping texture in everything you can see with the naked eye (often useful in lanscapes).
The only way to be sure of getting this shadow detail is to read the area in question directly, usually with a spot meter, using whatever EI and meter index you have found, by simple iterative experiment, to give you the texture you need. A properly designed spot meter doesn't even have a mid-tone index, because no speed system is based on a mid-tone. Instead it has a shadow index (for neg) and a highlight index (for tranny and digi). The mid-tone index is a pernicious invention designed to pander to those who don't actually know what they're doing, but work by rote instead. This includes a distressing number of Zone aficionados.
If there is no shadow index, you can work 2 or 3 stops down from the mid-tone index, or at any intermediate point between 2 and 3 stops: 2-1/3, 2-1/2, 2-2/3. Even 3 stops, at the nominal ISO, will often give you some texture. At 2 stops, you will always have texture. Obviously you can vary EI or index (2 stops, 3 stops, intermediate point) or, if you're a masochist, both: 3 stops down at EI 200 will give you exactly the same exposure as 2 stops down at 400.
Next, you want to make sure that the highlights aren't 'blown' to a featureless white in the print. You can usually do this by choice of paper grade, of (if you are wedded to a single grade) you can vary development time according to the brightness range of the subject: this is the Zone N-/N/N+ development time. Or you can split the difference via 3 dev times: what I call the 15/50 method, which works as follows.
You establish (via simple iterative tesitng) the dev time that gives you a good print of a normal subject on grade 2 to 3. For subjects with a very long brightness range (e.g. brilliant sun), decrease your normal dev time by 15%, and for subjects with a very short brightness range (e.g. heavy overcast) increase it by 50%. Then use VC paper again for fine tuning. If you don't like 15/50 use 10/40 or 20/60 or whatever works for you.
All this, of course, refers to wet printng. Once you're scanning, you have far more control. Your main limiting factor is the maximum density your scanner can see through. At this point, the Zone System and its jargon is even less relevant to what you're doing. In fact, if you have any sense, rather than piddling around with the Zone System you'll use XP2 Super (at whatever EI suits your metering technique) for its long, straight characteristic curve and absence of Callier effect, and sort everything else out in post-production.
Cheers,
R.
