... when I make a gray scale, the scale itself is centered around the exposure time that produces the Zone V negative to match the gray card. I'm only commenting on the production of a gray scale, ... I believe that power [of visualization] is derived by a fundamental grasp of the production of an accurate gray scale using ZS principles.
I've been cogitating about this for a while and have a couple of thoughts: I agree wholeheartedly that having a grasp of the grey scale is one of the fundamentals of learning to visualize. The problem I have with centering around Zone V is the possible lack of "accuracy" of the scale, or more precisely, the lack of correspondence of grey scale tones to meter readings.
I spend a lot of time coming up with an E.I. that gives me satisfactory blacks and the desired shadow detail in Zone III. Finding this is done visually, using proper proofing, and is subjective and a practical compromise between the two variables. (Stephen, I don't use 0.1 over FB+fog, nor do I obsess over achieving D-max in the printing paper -- in essence, I agree with you about the vagaries of proper proofing; it is a subjective tool and requires practice and a certain flexibility in application.)
Arriving at my final E.I. is a process of tweaking development time and exposure and making Zone Rulers (grey scales). As mentioned, I strive for an E.I. and development time that gives me a benchmark of sorts at Zone I (erring a bit on the side of overexposure if there is any question), detail in Zone III and Zone VIII and as close to a paper-base white in Zone IX as practical (all this for "N," of course; other parameters guide tests for expansions and contractions).
Therefore, my Zone Ruler for "N" is keyed to those parameters, which directly correspond to exposure values, i.e., to meter readings. I proper-proof the Zone Ruler, printing all shades of grey at the same exposure. My result is a grey scale that shows me the print values I will get at a particular E.I. and placement/fall of subject luminances. I try to keep the accuracy of the Zone Ruler exposures at 1/3-stop or better (try is the key word here).
So, my Zone Ruler is not matched to Zone V = 18% grey density, but rather to the speed point I have subjectively chosen. This usually results in a Zone V density that is not exactly 18% grey. However, the values on the Zone Ruler do correspond rather closely (within a fraction of a stop if I've been careful) to actual print values for a given meter reading. That, in a rather bloated nutshell, is my reasoning for not keying the grey scale to 18% grey.
Enough about Zone Rulers...
Back to the negative density vs. print value discussion. I was out shooting yesterday and worked with a subject that may provide a good example of what I'm trying to say about the flexibility of subject value placement and negative exposure vs. print value and the role of visualization in the process:
Subject: an old storefront/facade in glancing but veiled sunlight. The marquee is jet black glass that is really inky in areas of no reflection. There is also weathered wood (an obvious mid-point in my visualization) and a large white sign surface with black lettering. I place the darkest area of the black marquee in Zone II- (1/3 stop less than Zone II) and see where the other values fall. Oops, the value I wanted as a mid point falls in Zone VI-, whereas I would like it in Zone V, and the white surface that I would really like in Zone VIII is VII+; a bit low. Now, if I expand to get Zone VII+ up to VIII, I raise the mid-point that I want in Zone V as well; no-go... And, the luminance spread between my Zone II placement and my desired Zone V "mid-point" is too great. (A good example of reality not matching visualization.)
Solution: I really want to compress the distance between Zones II- and V, and expand the distance between Zones V and VII+ in order to get my visualized print, which is not possible with exposure and development alone, however. I, therefore, base my exposure on Zone II-, keeping the lowest values down on the toe but still giving me detail in Zone III. I also really want the white sign front in Zone VIII or a little higher, so I decide on a bit of expansion; N+1/2 in this case. This gets me a bit more density in the highs, but my mid-point now falls even higher than I want it. But, I've decided on an approach to printing already as well, which I note on my exposure record: Center print exposure on the mid-tone (essentially printing Zone VI and Zone V, which gets most of the values where I want them). This, however, dumps the shadows and results in the high values being printed too grey, so I plan to dodge up the shadows to compensate (I'll have good detail there, since I based my exposure on the lowest value), and deal with the still-a-bit low high value by either dodging or bleaching or a combination of the two. Often, in cases like this, printing a tad dark and then using an overall bleaching in a weak rehalogenating bleach gets the whites where I want them without affecting mids and shadows too much.
Point of the entire example: Negative densities correspond to no particular print values, rather I plan to use print manipulations to alter the "natural" scheme of things and print negative density values in other print zones than they would "fall." This is only possible because I am able to make an informed visualization of the scene based on my knowledge of materials and techniques. And, even if my planned strategy doesn't work, I can further refine my manipulations in the printing process to maybe still get a great print. (No matter how carefully I work, there are many more failures than successes in achieving a really expressive print. I believe, however, that I have a much better chance of success because I know what I want before exposing and have a good knowledge of the possibilities and limitations of the medium.)
Print zones are fluid and subjective and subject to many variables, as Michael points out. I think we can, however, really plan, or at least try to plan, what print values we want and craft a negative to allow us to do that.
Best,
Doremus