Metering Highlights for Roll Film
Back on my soapbox in defense of Mike's method again
Yes, the most accurate way of dealing with film is to place important shadow detail where you want it and develop for the proper contrast so that the highlights fall in an easily printable negative density. I use sheet film exclusively and this is what I always do.
However, there is sound reasoning behind exposing for the highlights and letting the shadows go in the case of roll film, where many negatives with different subject brightness ranges recorded on them are being developed for the same time. But, one critical compensation is necessary. Here is my entire case:
Let us look at three scenarios, a low-contrast scene, a "normal"-contrast scene and a high-contrast scene. Assume all of these are on the same roll of film, and will be developed in the same way, i.e. "normal" (I'll talk about what "normal" should be for roll film later). We also assume that the differences in contrast will be compensated for in printing by using different contrast printing papers instead of different development times for each scene as is possible with sheet film.
First, lets take the case of a low contrast scene that has only a three Zone subject brightness range (SBR). (This corresponds to N+2 in classic Zone-System terminology.) Metering and exposing for the shadows places the majority of the values low on the film's characteristic curve, reducing separation overall, and especially in the shadows (if you place the shadow on Zone III, then the "highlights" fall on Zone VI). When developed normally (our only available development), such a negative is thin and has little contrast. If one places the highlights in Zone VIII in such a case, the majority (or all) of the values fall on the straight-line portion of the negative (between Zones V and VIII), and have the maximum amount of separation possible. The only downside to this is that the negatives, being a bit more dense, will exhibit slightly more grain. This is a small trade-off for the increase in tonal separation and printability of the negative. A negative like this will still have to be printed on higher than normal contrast paper, but one has maximized the separation on the negative for the development given.
Now the normal situation. In this case, we have a 5-Zone separation between important shadow and highlight values; this is the scenario that the system should be calibrated to, and placing the highlight in Zone VIII allows the shadows to "fall" on Zone III where they should be. Notice that in this case, placing either the shadows or the highlights results in exactly the same negative.
Now for the high-contrast scene. Assume we have a 7-Zone spread (this is N-2 for us Zone System users, and a rather extreme situation). If we place the highlights on Zone VIII, the important shadow value falls on Zone I. This is where we lose the shadow detail.
BUT, and this is important, if we overexpose the film by two stops, then we have the shadows on Zone III, where they should be, and the highlights on Zone X, where they shouldn't be. However, we do have all the information on the negative and have not lost shadow detail. In this case, we rely on a low-contrast printing paper to take up the slack for the unwanted two-Zone expansion. We are relying here on the latitued of most modern films to retain separation in "overexposed" highlights. Some films are better at this than others, so film choice is a factor in optimizing this system. (My Tri-X retains highlight separation up to Zone XII.)
If the extra exposure is not given, shadow detail is lost, irretrievably, so it is very important to recognize this situation and compensate for it by "overexposing." That means one would have to be aware that the SBR in this case was two Zones wider than normal, and then place the highlight in Zone X instead of Zone VIII (i.e. overexpose two stops from the "normal" highlight placement. For a SBR that was one Zone wider than normal, a one-stop overexposure would be given).
Note, that to use the above system effectively, two things are critical. First, one needs to be aware of the contrast of the scene one is shooting, at least to the point of recognizing overly-contrasty scenes so that one can overexpose (i.e. compensate for the shadows falling too low) by the proper amount. This means one still needs to meter highlights and shadows and determine the SBR in contrasty cases. (For low-contrast and normal scenes, simply metering the highlights will do, but if there is any doubt, find the SBR).
Second, it helps if the entire system is calibrated to a higher-than-usual contrast paper. In other words, "normal" development should be calibrated to grade 2.5 or 3 paper, not grade 2 as most sheet-film-Zone-System users do. This ensures adequate paper grades on either side of normal as well as establishes negative development to a slightly lower contrast, thus allowing the overexposure needed for high-contrast situations to result in a relatively lower density for the highlight densities, thus making them easier to print.
With this system, so calibrated, I can shoot scenes from N-2 through N+2 on the same roll and still have printable negatives in all cases. Not only that, but the low-contrast scenes will actually be rendered more printable than if I had placed the shadows on Zone III and given the same development. I believe that this is an excellent practical application of the Zone System to roll-film formats. Yes, it is a compromise, but, I believe it is a compromise that has very few disadvantages.
Notice that I am not ignoring the shadow values here, but rather that the system is based on metering and placing the highlights, compensating where needed to ensure that the shadow values have the optimum printable density for the given development.
Of course, if one has interchangeable backs, one can have three or five different backs, each dedicated to a different development. This, however, often becomes "fumbly" and slow, and defeats one of the purpose of shooting roll film in the first place, that of speed and flexibility.
A modification of the above might be to keep a separate film back or camera body for contrasty situations, designating this for a contraction development somewhere at about N-1.5. That would at least reduce the fumbling around to just two things.
One word about "pushing." When shooting hand-held roll-film cameras in low-light situations, such as night clubs, concerts etc. one often intentionally sacrifices the shadow detail for usable shutter speed. In these cases, the film is "push-processed," i.e. overdeveloped, to move highlight values to a reasonable printable density. Like the above scenarios, highlights are metered and "placed" where they will come out when the film is overdeveloped. The shadows in cases like these fall where they may, and usually lose all detail.
"Pushing" like this is a case of
underexposure and overdevelopment, not the
overexposure and overdevelopment that I am advocating for contrasty situations in order to retain shadow detail. (It is, however, what would happen if one did not compensate for the extreme contrast by overexposing).
Remember, all this is based on metering and placing the
highlights. The entire way of thinking about this changes when one meters and places the shadows. So terms like "overexposure" and "overdevelopment" have different meanings in this context.
Finally, a word about transparency films: With slide film, the highlights are the least-dense part of the final product. Exposing for highlights in this case is analogous to exposing for the shadows with negative films. There are many who shoot transparencies with a modified Zone System based on the characteristics of these materials. Others, who do not manipulate the development of transparencies simply let the shadows fall where they may, favoring highlight detail over empty shadows in a similar fashion to what I have described above.
Hope this helps some of the roll-film users out there.
Best,
Doremus Scudder
www.DoremusScudder
