Zone System Thinking:
Knowing the meter values I could now use this information to think about how to manipulate the tonalities to be more like what I saw in my mind.
My thoughts followed these steps which I have attempted to color coordinate against the photograph so it can be understood how the decisions affect all values.
Black: These were my initial meter readings with a Key Stop of f/32. These readings are a reflection of the tonal values in reality and serve as the launching board for all my subsequent decisions.
Yellow: If I exposed the photograph at an 1/8th of a second than the underside of the clouds would be on Zone V or neutral gray and the other tones would fall into the zones as noted in the photograph. I felt that placing the underside of the clouds at Zone V was too light. I wanted them dark and dramatic so I decided to begin by moving all the values down by one-stop or one Zone. Now my base exposure is 1/15 of a second.
First, I consider what this has done to my shadow detail. This moved the buildings in front from Zone III to Zone II. This means they will retain detail but will be very dark, lurking, actually. This is fine with me since I don’t really care about the buildings and they can lurk all they want at the bottom of the print.
Next, I look to my highlights. My delicate highlights in Zone VII ½ have shifted down to Zone VI 1/2, which is too gray and muddled in my opinion. I want these to have a light delicacy and luminosity so I need to find a way to move these values back up to the higher zones. The white hotspot has moved to Zone VIII which is just within detail reach, but knowing that this scene will be contrasty, and that I will need the whitest white I am going to compromise, give up on retaining these values in the print and let them go. This is a critical decision someone may handle differently, but at that moment I wanted to let these silver linings be the white of the paper in the final print and let the less intense linings be white and not feel stifled.
Orange: Looking now at which parts of the scene fall in which Zone I find I am satisfied with everything in Zones 0 to Zone V (black to neutral gray). However, the areas of the scene I want as delicate highlights are far too dim now, but I can change this with the development of the negative. To move the delicate highlight values back up I decide to push the sheet of film one stop. This will result in a number of changes to my image:
1) Overall contrast will increase. This helps not just with the clouds but with the rays of light which I find to be visually subtle.
2) My highlight values will be lifted up by one Zone or one stop. This means some detail will be lost, but other areas that are being suppressed will be lifted, and the increase in contrast will further sculpt these delicate contours.
Decision made I look at how this will affect my Zones. My Zone II area in the building will remain the same since I am basing final exposure on exposing for this shadow area. (Remember the old adage; “expose for shadows, develop for highlights.”) I look to my highlight area and with the one stop push it will go back to Zone VII ½, which is exactly where I want it. (I know from tests that Zone VIII is the tone of just barely paper white with my materials.) I look to my middle areas where the one-stop push is not going to be as effective (pushing one stop does not affect all tones in a linear fashion, but affects highlights most) so it will probably land at around Zone IV ½.
Red: This is all well and good, but the decision to push is shifting my tonalities in a way I feel I needed to compensate for. I want my clouds at Zone IV, not IV ½ so I decide to move my Key stop to f/32 ½. Looking over my values again I find this suppresses the buildings by another ½ stop, which I am not overly concerned about since I felt I could let them become a silhouette if necessary. This also moves my delicate highlights to Zone VII, which is a very safe area to preserve delicate cloud tonality. After all, if I feel the print lacks punch I can change the paper grade.
So my exposure decision at this point is 1/15 @ f/32 ½ with +1 (Push one stop) development.
What follows is rote execution of what I know about my materials from Zone System Tests. Looking at notes I note what ISO (or precisely E.I. at this point) I must rate my film at for +1 development and adjust my f-stop or shutter speed accordingly. Later, these same notes also give me the developing time for the sheet.