Zone System Calibration (Parts I&II)
Part I: A Conceptual Foundation
©Copyright 1991 thru 2008 David Kachel
Article First Appeared in Darkroom & Creative Camera Techniques in Sept/Oct 1991
No aspect of the Zone System is more plagued by misunderstanding, misinformation and misguided pseudo-science than calibration (with its attendant ideas and methods). In this two-part article I hope to do what I can to put the calibration part of the Zone System's house in order. Part II will present a new method for calibration which I believe to be a leaner, easier, far more reliable, and accurate calibration method than any currently in existence. In this first article, I will address the conceptual basis for calibration methods in general, a subject sorely in need of attention.
Zone System calibration, as currently taught, is defective to its core. Those fundamental truths that should be the backbone of any calibration method not only do not occupy such a position, but in most cases are given only lip service if mentioned at all, and worse, are often simply contradicted. Some calibration methods have gone so far astray from any scientifically valid premise that they have actually produced profound misunderstandings about the theoretical underpinnings of the Zone System. This peculiar case of the means modifying the end necessitates that before proposing a new calibration method I must examine onebyone, the aforementioned fundamental truths so that we may first lay a proper foundation. I feel that no method of calibration can be considered valid unless it takes into consideration the following essentials.
Any approach to calibration must be based on a solid understanding of the purpose of the Zone System.
The purpose of the Zone System is to aid and enhance the photographers visualization process, while granting maximum freedom of expressive interpretation of the subject.
By way of support for this purpose, the Zone System imparts an understanding of what is, and is not physically possible to produce in a photograph. And it provides the necessary knowledge and skills to consistently turn those sophisticated visualizations into high quality printable negatives.
It is unfortunate indeed that the purpose of the Zone System can be so readily misunderstood by newcomers and even some ill-informed, though well-intentioned teachers of photography. Nonetheless these misunderstandings are indeed very common, and I therefore feel I ought to include a statement concerning what is not the purpose of the Zone System.
Toward the end of maximizing control, it has long been advised that the density range of ones negatives be geared toward a middle contrast range grade of paper, usually a grade 2. However, this is not to say that the negative is actually intended to be printed on that paper, a misunderstanding easily acquired. There is no special virtue in printing on any particular grade of paper. Gearing negatives toward grade 2 paper serves only to guarantee that negatives will fall approximately within a middle range of paper grades, assuring options for both lower and higher grades at the time of printing. (There are times when it is more advisable to gear specific negatives toward some other grade of paper. See The Primacy of Local Contrast.
There is no point whatsoever, nor was it ever intended, that the Zone System photographer should try to achieve negatives that can all literally be printed on one specific type and grade of paper. This is not in any way part of the purpose of the Zone System. A negative should be printed on the grade and type of paper that renders it best, regardless of the negatives density range and the papers exposure scale. Because Zone System negatives will invariably be subjected to a highly creative act of printing, they will likely as not be printed on some grade of paper other than grade 2, or otherwise subjected to extreme tonal manipulation, nullifying any precise density range to paper curve match that might have existed beforehand.
Let me repeat: Under no circumstances is it part of the purpose of the Zone System to literally match the density ranges of negatives to a specific papers exposure scale.
The Zone System negative is not intended to be tailored to a certain type of paper, but rather to a certain type of print. The purpose of a Zone System negative is to lend itself well to producing the kind of print envisioned by the photographer at the time the shutter was released and not to match any rigid, predetermined concept of an ideal negative. This fundamental truth must be a cornerstone for any approach to the Zone System and calibration.
Finally, the purpose of the Zone System is not, as believed by some, to faithfully reproduce in the print a literal representation of all the tones as seen in the original subject. Were this the case, the Zone System would be a largely unnecessary burden.
The Zone System is a tool for creative interpretation that allows the photographer to carry tone and contrast manipulation to the technical limits of the medium; exactly opposite the anemic idea of tone for tone, literal, robot-like duplication of grays and matching of scales. The Zone System assists you in producing a photograph of what you see in your mind, not of what you see!
Any Zone System calibration method must take into consideration the extreme importance of the photographers ability (or inability) to correctly analyze a subject. Careful calibration and preparation mean absolutely nothing if the photographer cant correctly analyze a subjects reflectance range and contrast needs. Dont forget that calibration methods are aimed largely at the beginning Zone System photographer The experienced photographer has long since settled into comfortable calibration methods and shortcuts.
Due to inexperience at analyzing the subject, a newcomer cannot help but give incorrect exposures and assign mistaken N numbers (i.e. N+1, N-1, etc.) to a substantial percentage, if not the majority of subjects. These mistakes often lead to significant and sometimes severe errors in film development which unfortunately are all too easily blamed on inadequate calibration methods. This leads the newcomer down an endless mistaken path in search of more precise calibration, instead of searching for more experience.
The single most difficult and important part of Zone System photography is learning simply, to correctly analyze the subject before the camera. Any approach to Zone System calibration must place this extremely important aspect above all others by helping the newcomer learn to adequately analyze subjects while calibrating, and at the same time not allow errors in subject analysis to lead the calibration process astray.
Although negative-making is critical, an equally (if not more) important creative skill is the ability to make an excellent print. The Zone System can help provide a good negative, but it cannot teach someone to print it. Any approach to Zone System calibration must take this into account.
It is very easy to fall into the mistaken belief that having mastered the Zone System, your prints will be beautiful. Nothing could be further from the truth. The myth that a good negative automatically produces a good print is just that, a myth. A good negative can only make it possible to get a good print; it doesnt guarantee it. The better the negative, the more easily a good printer can make a high quality print. However, a poor printer cannot get a good print from any kind of negative. In this instance, Ansel Adams musical metaphor is most appropriate. A skilled and talented printer is just as necessary to the performance of the score of even the very best negative as is the similarly gifted musician to the excellent rendering of a musical score.
To be valid, any Zone System calibration approach must take into consideration the fact that the Zone System is no substitute for skilled, creative printing. It must also consider that someone who is learning the Zone System will almost certainly be learning to print at the same time. Since a newcomer will have to learn two important skills at once, I believe that a calibration method should be capable (if needed) of helping the newcomer learn to print and calibrate at the same time. This can be done by making the act of printing real negatives a necessary and integral part of calibration.
Before proceeding with the next subject I would like to state more strongly, a generally implied point made in this and the previous section. Both have dealt with the topic of experience, first at analyzing ones subject, and then experience at printing. To be certain of clarity, let me state emphatically: The Zone System is not a substitute for experience. It is not possible to replace experience with the act of calibration. There is absolutely no way to avoid the fact that producing a good photograph is a skill learned through long, hard experience and not a mechanical cookbook style production process. There is no such thing as photography by the numbers.
Before any attempt can be made at devising an acceptable calibration method, it is imperative that the role of sensitometry in the Zone System be precisely defined. Many Zone System photographers use sensitometry, and the Zone System itself is heavily based on information provided by the science of sensitometry. As a result, not discussing sensitometrys role in the Zone System would be negligent in the extreme.
Sensitometry is a branch of applied physics that deals with the study of the effects of radiant energy (particularly, but not limited to visible light) on the behaviour of photographic emulsions. In the practice of sensitometry, a photographic emulsion is exposed under precisely controlled, reproducible circumstances, to light of known quantity and quality. The emulsion is then developed under controls equally as rigid and repeatable and the results analyzed through the study of the characteristic curves derived from densitometer measurements.
The science of sensitometry can and does provide the Zone System photographer with a great deal of invaluable information about the characteristics of photographic materials under a variety of circumstances. It is imperative that the Zone System photographer understand the basic principles of sensitometry and be capable of reading a characteristic curve. It is from this point of departure however that much misunderstanding has occurred.
Many Zone System photographers are mistakenly using sensitometry as a tool to predict the future behavior of photographic materials. Sensitometry can only describe the behavior of a specific light sensitive material under specific, highly controlled circumstances of exposure and development. From that description the sensitometrist can sometimes make reasonable predictions about the behavior to be expected from that same material under different conditions, providing that only one or two parameters at most are changed at a time, and only under the most rigidly controlled circumstances. However, the rules of science are no different for sensitometry than for any other science and wish as we might that it were otherwise, sensitometric measurements absolutely cannot give anything more than the most general indication of how an emulsion will behave when subjected to the drastically different and unpredictable circumstances of real picture making.
Calibration by means of sensitometric measurements of stepwedge or gray-card exposures is therefore of scientifically dubious value at best and can provide information likely to be no more accurate than a reasonable educated guess. It should be obvious that sensitometric measurements are not directly applicable to the practical task of Zone System calibration.
Lest I be misunderstood, let me state unequivocally that I am in no way denying the usefulness to the Zone System photographer of the tool of sensitometry. However, in my opinion, the tool has been used incorrectly by many. The only legitimate use for sensitometry in the Zone System is the same use employed by sensitometrists. That use as stated above is: To describe the behavior of a specific light sensitive material under specific, highly controlled circumstances of exposure and development.
For example, it is perfectly acceptable to use sensitometry for process control. Film can be given a stepwedge exposure in the darkroom under repeatable lighting conditions and then developed along with real negatives. In this way, the stepwedge negative will be known to have received identical development to the real negatives that were processed along with it, and can then later be compared to a similar, future test, in order to be certain that ones processing remains consistent. In fact a number of stepwedge negatives can be exposed at one sitting and frozen for later process control testing.
The same stepwedges can be used to test new developers. Once a development time can be found that produces the same contrast as the old stepwedge test, it is safe to assume that real negatives developed identically in the new developer will have the same contrast as real negatives developed in the old developer.
Stepwedge tests of new films made at exposures identical to the exposure employed for the original stepwedge test, could also be used to determine the approximate speed and contrast to be expected from the new film, prior to field testing.
There are a lot of legitimate uses for sensitometry both for the Zone System photographer and for those who dont employ the Zone System. One of those uses is not however, to predict how an emulsion will behave at dawn on top of Mount McKinley, based on how it reacted to a stepwedge or gray-card test made on a Thursday afternoon in Iowa!
Just exactly how precise can and does calibration need to be? A favorite analogy may help put the problem in perspective.
Rather than use the customary two dollar kitchen scale, a gourmet chef might instead choose to weigh out ingredients on a chemists glassenclosed precision laboratory balance, costing several thousand dollars, last I heard. Although a scientific balance would make the new procedures (weighing out ingredients) more precise and perhaps make the chef feel very scientific, it would produce no real improvements in food quality. Measurement in the culinary art requires no greater precision than that provided by teaspoons and pinches.
Only a level of precision that produces useful improvement in the end product is worth considering. All degrees of precision beyond that point (i.e. those which do not significantly improve the product or at least make its production easier) are complete wastes of time and effort. We must avoid making Zone System calibration mistakes similar to those made by our chef.
It is both possible and common to employ more precision in Zone System calibration than can be justified by the resulting improvement in ones photographs. The temptation to apply unnecessary precision most often springs from the mistaken belief that the purpose of calibration is to reconcile all of the variables involved in producing a photograph, thereby simplifying the technical aspect of photography into a cookbook type procedure. Nothing could be further from the truth, or less possible. There are so many variables involved, many of which are not only unpredictable, but also completely beyond our control, that any attempt at all-encompassing calibration is certainly doomed to failure.
Following are just a few of the factors that will nullify any attempt at precision calibration:
The above brief selection from the very long list of factors that make useless any attempt at applying precision, is nothing when compared to the most devastating and unpredictable variable of all: FLARE!
Flare is a multi-headed dragon indeed. It wouldnt be so bad if we had only to contend with lens flare. Lens flare is easily measured and figured into calculations, but there are other varieties of flare that are totally unpredictable, cannot be measured, and have a very substantial influence on our photographs, very often cutting density ranges by 50 percent and more. These include camera flare, flare produced by a bright object outside the image area but inside the field of view of the lens (partially controllable through the use of a lens hood), and flare caused by a bright object inside the image area (absolutely uncontrollable). This last variety of flare is the biggest spoiler of illusions for precision calibration. In particular, it makes the idea of calibrating for all but the mildest contractions, ridiculous in the extreme. For contractions of approximately N-3 or greater, flare will cut the final density range substantially, making any previous calibration efforts totally meaningless.
I could write an entire article on flare alone, but it will suffice to say that every photograph we make is to some extent significantly affected by flare. Any calibration method we use must take this unpredictable factor into consideration. Neither of the two major Zone System calibration methods stepwedge and gray-card testing incorporate flare. (To be fair, I must mention that some methods do include a lens flare factor in curve drawing. Although this certainly can be applauded, it still ignores the other, more substantial types of flare.)
The foregoing discussion leads us to the obvious conclusion that precision calibration is nothing more than an enticing illusion. The purpose of calibration cannot possibly be to account for all existing variables.
The purpose of calibration is to provide a predetermined development time for each class of subject reflectance range the photographer is likely to encounter, such that all negatives in each class will have density ranges that on average, approximately match the exposure scale of a middle range grade of paper (usually grade 2), and nothing more. As to the question of precision, it should now be obvious that no more precision is required (nor possible) than that which is necessary to provide the type of negatives mentioned above.
It is easy to fall victim to the flawed logic that because sensitometry is precise, Zone System calibration both can be, and needs to be precise. But it is not precision of method we require so much as precision of understanding. The quality of the final product is far more dependent on the skill, knowledge and experience of the photographer than on the precision of the means employed.
To my knowledge no one has ever discussed the possibility of limitations to Zone System calibration. Indeed, Zone System calibration does have limits. These limitations reflect on the very credibility of any calibration method, and have to do with the extremes of contraction and expansion.
With contraction in particular, the greater the contraction, the more meaningless it is to talk about calibration. With contractions of about N-4 or greater, several of the original exposure Zones can become compacted onto the same negative density Zone. When three or more exposure Zones end up with Zone VIII densities (i.e. 1.25, 1.30, and 1.35), how can anyone possibly tell which contraction was actually achieved? If the original exposure Zones were XIII, XIV, and XV, this contraction could plainly be N-4, N-5, and N-6, all at the same time.
Now throw into this discussion the fact that flare will completely disrupt any possibility of predicting the density ranges of contraction negatives because flare unpredictably and drastically cuts those density ranges. As a result, calibration is impossible and pointless for contractions greater than about N-3. At this level, the Zone System concept of calibration simply disintegrates.
Extreme expansion presents difficulties similar to contraction, although flare is not a significant problem with most expansion negatives. In Zone System expansion FIlm, I showed that expansions greater than N+2 require the use of moderately high or high-contrast films. With these films, slight changes in development and exposure produce dramatic changes in the final density of any given exposure Zone. As a result, it is very easy for an intended N+4 negative to become an N+3 or N+5. It is often difficult or impossible to know what treatment was really given: While one part of exposure Zone V may be expanded to a Zone VIII negative density, another subject tone falling slightly higher on exposure Zone V may be expanded to negative density Zone IX. Yet another Zone V reflectance may only reach density Zone VII! In addition, with these higher contrast films all Zones are affected by development changes, leaving us with little in the way of traditional Zone System reference points when talking about exposure placement and expansion.
It is my conclusion that expansion and contraction extremes cannot be calibrated in advance and must be dealt with on an individual basis. In both cases I recommend exposing multiple negatives and performing experimental processing to determine ideal development under the circumstances.
The foregoing discussion certainly makes the Zone System and calibration appear to be a giant mass of contradictions. What can be done with a system of photographic control that apparently cant be precise? Likewise, how can we be in control when there are so many unpredictable variables to foil our attempts at control? Finally, how can we learn a system of control when it seems necessary to have mastered the system before learning it?
All of these seeming contradictions are overcome when we remind ourselves that the Zone System is not intended to be a device for the impossible task of holding reign over all the variables found in the practice of photography. Rather, it is a system of control employing, as do most effective systems of control, negative feedback.
For the uninitiated, a negative feedback system is one in which the results of a process are constantly used to determine corrections to that same process. For example, you steer a car by negative feedback. The car is never actually held on a perfectly straight course, but is constantly steered in small degrees, first to the left and then to the right. As a result, on average it stays on course. A negative feedback system is most beneficial in cases where unpredictable variables can be expected to cause constant and random deviations from the goal. Rather than attempt to control variables that by definition cannot be controlled, they are simply ignored and attention is directed only to results. Results are used to indicate any course corrections. It is an excellent device for controlling the seemingly uncontrollable.
The fact that the Zone System employs negative feedback means that no calibration method can be truly effective if it is based on stepwedge or gray-card testing. Both of these methods perform tests with virtually all of the previously mentioned unpredictable variables removed. Since a negative feedback system is a means of controlling unpredictable variables, any attempt to calibrate such a system with those variables removed is pointless. A truly effective Zone System calibration method must allow testing to occur while making real photographs, with all of the idiosyncrasies of hardware, film, subject, and photographer playing a role. I will present such a method in Part II.
©Copyright 1991 thru 2008 David Kachel
Article First Appeared in Darkroom & Creative Camera Techniques in Nov/Dec 1991
In Part I, I promised a new method for Zone System calibration that would take into consideration a number of fundamentals. I consider these fundamentals to be a necessary foundation for any valid approach to calibration. For more information, please refer to Part I.
If I make no other point in this article, I feel it is most important to say that Zone System calibration has in the past, been grotesquely over-emphasized. In virtually every form and approach to the Zone System with which I am familiar, calibration seems to occupy a central position. I am adamantly opposed to this. In every method, the newcomer is told to first calibrate and then photograph. This is nonsense. A photographer must first, last and always, make photographs (Kachels Law). Calibration should not be a separate undertaking, but should be done while making real photographs and should be a natural outgrowth of making those photographs. I urge you to adopt this approach to the Zone System and calibration.
There are a wide variety of approaches to calibration, from very simple, to highly complex and hardware intensive. Perhaps as many different calibration methods exist as there are those who teach the Zone System.
One of the things I hear often, from both workshop participants and readers, about other approaches to calibration that they have been taught, is that once they had completed the (often very tedious) process of calibration, they found their negatives did not deliver what the calibration method in question had promised.
The reason for this is that too many approaches to calibration are based on invalid assumptions and pseudo-science, and are too centered around the approach itself, rather than the results. By centered around the approach, I mean that the calibration method often seems to be its own reason for existence and takes on a life of its own, whether or not it actually results in improved negatives.
From a practical standpoint, there is only one valid measure of whether or not a calibration method is effective, and that is How do the negatives print?!
It is irrelevant how seemingly scientific and precise any given method of calibration may be. The only thing that matters is whether you are getting the kind of shadow and highlight detail you are seeking in your prints. If not, then the calibration method is invalid, regardless of how precise and scientific it appears to be. The only thing that matters with calibration is results!
My calibration method is based on the reasonable assumption that the person doing the calibration is a newcomer to the Zone System and will commit frequent and substantial errors. Ive designed my approach to help the Zone System beginner see those errors and learn from the experience. Toward those ends my method is intended to allow errors to take place in a controlled manner, causing specific types of errors to occur under specific conditions so that they will stand out in relief against a static back-drop. In fact, the assumption of error is an essential part of my approach. At the same time, the method allows the seasoned Zone System photographer to bypass experiences already acquired.
It is my belief that learning in photography is vastly aided by going too far (committing errors). Nowhere is this better illustrated than in the act of making a print. The easiest way to be sure of the right contrast in a print is to have a variety of prints, among them one that is definitely too flat and another that is absolutely too contrasty. When these recognizably unacceptable extremes are present, it is a much simpler matter to select the best contrast from the samples between extremes. You may recognize this as simply another way of describing negative feedback. In Part I, I defined negative feedback and explained that it is the ideal way to control the uncontrollable (i.e. the Zone System and calibration, a system plagued by unpredictable variables).
With a negative feedback system you can begin absolutely anywhere and, knowing the goal, immediately begin steering in the right direction. However, it is senseless to begin at a point known to be far off course, so a certain amount of reason should be applied when selecting a starting point.
I do not ascribe to the idea some Zone System experts have of making a mystery, almost a holy grail, out of the concept of your film speed or your development time. These are simple, non-mysterious issues and should not get in the way of the numerous far more important aspects of the Zone System.
I do not consider it cheating, or giving away the end of the story, to inform students that most Zone System photographers end up using a film speed for N subjects that is about half the manufacturers recommended speed, i.e., EI 200 for an ISO 400 film, EI 64 for an ISO 125 film, etc. (This does not apply to transparency films.) I also warn them that any significant deviation from this speed should be taken as a very strong indication of error and should make them suspicious of either their methods or equipment.footnote 1
In order to test film speed, the film has to be developed. Since we have not yet determined a Normal development time for our film, we will have to make an educated guess at an approximately correct development time, just as we had to guess an approximate starting film speed.
As with starting film speed, I do not agree with the idea of making development time something mysterious. There is no reason not to benefit from the experiences of those who have gone before, and those experiences make an accurate first guess very likely.
For a starting N development time, take whatever time the manufacturer recommends for the selected film/developer combination and cut 30-percent from that time for all types of film except T-grain films. For T-grain films, cut only 20-percent because these films are more sensitive to development changes. Like my recommended film speeds, these development times approximate the times most Zone System photographers end up using. The final development time derived for N negatives may vary substantially due to the significant differences from one worker to the next in the way film is processed, i.e.: type of tanks or trays, form of agitation, etc. However, once again be very suspicious of equipment or methods if your final time varies more than 30-percent from the starting time recommended above for ordinary film or by more than 20-percent for T-grain films.
The experienced Zone System photographer can look at a negative and know whether it has been over or underexposed and/or over or under-developed, and by approximately how much. The Zone System beginner can do neither of these things. So it is logical while determining a working film speed for N subjects to simultaneously teach the newcomer how to visually recognize correct exposure. The method for doing this is very simple. Here is how to determine film speed:
First, follow Kachels law. Make real photographs! You need do nothing different from what you might ordinarily do, except to shoot some extra negatives at bracketed exposures and of course, apply some of what has already been learned about the Zone System.
Shoot any subject that interests you, N, N+ or N-, but calibrate only for one N number at a time. To do this, simply separate the bracketed negatives of your N subjects (or whatever N+ or N- subject class for which you happen to be calibrating), for testing. N+ and N- subjects, though still photographed, are simply excluded from consideration for calibration and for the time being, are treated as you have always handled them in the past.
In addition, only N subjects for which you do not use a filter (with the exception of a polarizer) and for which you have placed important shadow detail on Zone III, can be used for calibration. If important shadows need to be placed on some Zone other than III, shoot the subject anyway, just dont include it in your calibration efforts.
Using the starting film speed determined previously, bracket identical shots of each subject you have analyzed as Normal by 2-stop increments up to 12-stops on either side of the starting speed. If using a starting speed of 200, bracket shots at 75, 100, 150, 200, 300, 400 and 600. Again, include only N (normal) subject reflectance ranges in this testing. (Later, you will repeat this procedure for N+ and N- subjects.) Base exposure for each subject on what you consider to be a large and clearly defined Zone III shadow tone in the subject. Small Zone III areas make judging calibration tests difficult and inconclusive. If unsure, go ahead and shoot the subject, just dont include it in this test.
As already mentioned, it is absolutely vital that filters not be used on any of these test shots. If a filter is needed, once again, go ahead and take the photograph with the filter, then make your test series of photographs without it.
To be truly effective when starting out, you need a minimum of 10 to 12 different bracketed subjects. But more is better, and since these are real photographs, some of which may end up in your portfolio, 100 isnt too many. Now develop.
Give the starting N development time described earlier to all of the negatives. Film speed will be determined by printing.
Since film speeds change with changes in development, you may think this approach is inaccurate. In fact, substantial changes in development time are likely to produce film speed changes no greater than ±2-stop. Therefore, later adjustments to this starting development time will likely have little or no effect on speed. If significant adjustments to development time are made, you may wish to re-check film speed.
To determine speed for this film, print each of the bracketed negatives for each shot. To save paper, I suggest making 32 x 5 or 4 x 5 prints. I recommend the following steps:
First, print the least exposed negative. (In the bracketed series suggested above, this would be the negative shot at EI 600.) Make the best straight print you can from that negative on your customary grade 2 paper. (For the moment it is irrelevant if the negative would print better on some other grade of paper. Remember from Part I that we are trying to aim negatives in general at a generic grade 2 paper, even if we wont really be printing them all on that grade.) Make a good straightforward, non-interpretive print that shows the most detail possible in the shadows without being too light. (Remember you are trying to print a Zone III tone.) Ignore the highlights and how they look, completely.
Next, print all the other bracketed negatives of that same subject in increasing order of exposure. In each case, try to get the very best shadow detail possible, while remembering to print the shadows of each negative at the same general tone of gray as the first. Now compare all the prints.
Assuming a starting film speed of 200, compare the print from the EI 400 negative to the EI 200 print. If the shadow detail in the EI 400 print is not as good as the EI 200 print, then a film speed of 400 is too fast. If it is just as good, or better, compare the negative shot at 600. The 600 speed negative should absolutely produce inferior Zone III details and be noticeably underexposed. If that is not the case, dont panic yet. Remember, this method presumes you will make mistakes and is designed around them.
Next, compare the print from the negative shot at 100 to the 200 print. If it is not demonstrably better, this speed (100) is too slow. If it is noticeably better, compare the print shot at EI 75.
Finally, compare the prints from the negatives shot at 2-stop over and under the starting speed, to the starting speed print.
In comparing all the prints from this bracketed series of one subject, you will probably find that several of them have similarly good shadow detail and contrast, and that it is difficult to determine which is absolutely better than the others. (Doubts are OK and expected.) Remember that one of these prints will represent optimum negative exposure for the particular subject photographed. Prints made from negatives having received more exposure than this optimum will have shadow detail just as good and will therefore be indistinguishable. Make a note of the speed used for the fastest negative that gave good shadow detail. If, for example, you got equally good shadow detail from the negatives shot at EIs 300, 200, and 150, note a speed of 300 for this particular subject.
With some subjects, it will be fairly easy to distinguish which negatives gave the best shadow detail. With others, it will be difficult and perhaps frustrating. This is normal, and simply supports my contention that the Zone System and calibration cannot be precise.footnote 2
Now print and record speeds for all of the bracketed negatives for all of the other subjects (10 to 12 or more) you shot. Dont be surprised to see that the best speed for the next subject is 200 while the one after that may be 150. Remember, small errors in exposure and subject evaluation are expected to happen, and variables beyond our control will always enter into the process.
With time you will become able to visually determine that some of the negatives in a test group are obviously too under or overexposed to be bothered printing them. At first, only the most extreme examples will be obvious to you, but with practice you will be able to judge exposure by eye alone.
Determining your final film speed is now very simple. Drop one each of the highest and lowest speeds resulting from your tests and average the remaining numbers. (If you dont have enough subjects for a good sampling, just save these results until you can get more.) Round the result to the nearest 3-stop speed point. If the result is midway between speeds, use the slower speed.
Expect to get a final speed within ±2-stop of the starting speed. If you do not, use whatever speed you determined, but shoot more bracketed negatives in the future and add their results to your average.
You now have the best N film speed for the way you determine exposure under real picture making conditions. You will continue to make exposure errors, but half of your errors will be above this point and half will be below it. As you gain experience you will narrow the range of those errors to a minimum.
The next step is to deal with errors in subject evaluation, while at the same time, determining an N development time.
When we originally began shooting our test negatives we selected a starting development time based on a percentage of the manufacturers recommended development time for the filmdeveloper combination we are using. We must now evaluate that time to see how close to correct it is for the class of subject/negative (in this case Normal) we are testing. This is very simple to do. (Chances that this starting time will be significantly off are quite slim.)
For each subject, select the print you made while determining film speed that represents the correct speed for that particular subject. In other words, if you determined that an EI of 200 was the correct film speed for a particular subject, select the print from that EI 200 negative.
Examine the highlights of each print, and sort the prints as follows:
Place the prints from all negatives having good highlights in one pile, all those having highlights that are too light in another, and all prints having highlights that are too dark in a third.
At this point a small problem arises. There are three reasons why highlights can be too dark or too light in these prints:
You must now determine which of the three possibilities above is the case. Heres how to do it:
Start by reprinting all the optimum film speed negatives that showed dark highlights in your initial prints. This time, print the negatives on grade 3 paper, and expose for best shadow detail, exactly as you printed them initially. If this produces a print that still has too dark highlights, that subject and its negative should be eliminated from calibration You can assume you made an error in evaluating the tonal range of the original subject, or that your starting development time was substantially off (i.e., this negative should have received N+1 or even N+2 development).
The subjects in this grade 3 print group showing highlights that are no longer too dark should have their original grade 2 prints returned to the group of prints previously classed as having too dark highlights. These subjects were correctly evaluated, but are simply one extreme of the Normal group.
Next, print any negatives with highlights that were too light in the initial prints on grade 1 paper. After printing, discount as errors in initial subject analysis, or in your development time, those prints that still have too light highlights. Return the original grade 2 prints for the remaining subjects, those that do exhibit good highlights on grade 1 paper, to the original group of too light highlight prints. This group represents the opposite extreme of Normal.
You have now eliminated all prints of subjects likely to have been incorrectly analyzed (there is room for error here). All that remain are prints from N subjects, more or less correctly analyzed. You will again have three groups of prints as mentioned above: dark highlights, light highlights, and good highlights. But, few or none of these will be from incorrectly analyzed subjects.
Next, eliminate the print with the brightest highlights and the print with the darkest highlights. In case of a tie, use the eenie, meenie method. The purpose of this is to remove wild cards from consideration.
At this point if you have for example, six prints in the good highlight pile, and three in each of the other two piles, then you hit the development time right on the head and neednt go any further. Your development time for Normal subjects is, on average, correct.
If almost all of the prints are in the pile having highlights that are too light, decrease your N negative development time by 2030-percent for regular films and 1020-percent for T-grain films.
If almost all of the prints are in the pile having highlights that are too dark, increase your N development time by similar amounts.
If you have only a slight bias in one direction or the other (too light or too dark highlights), make a smaller adjustment in your negative development time (5 to 10-percent).
Finally, in the unlikely event your starting development time was substantially incorrect, none of the forgoing print sorting will have been possible. Instead, all of your prints will have highlights that are too dark or too light, and will not be split between the two extremes. They will all be substantially at one end of the spectrum or the other and most will not be rescued by printing on higher or lower paper grades.
If your starting development time was significantly too long, then most of your test prints will have highlights that are too light and remain too light even when printed on grade 1 paper. If your starting development time was too short, then all or nearly all your test prints will have too dark highlights that will still be to dark after printing on grade 3 paper. Alter your starting development time by 2030% (up or down) for future N subject tests, and start over.
If this all sounds imprecise, remember that you are looking for an average development time for a group of negatives, not for a time that is exactly correct for all of them (something we now know to be impossible). After adjusting your development time based on test results, you neednt go back to test again unless you had to make a large correction, or see that an inordinate percentage of your future negatives are over or under-scaled for a grade 2 paper.
Please keep in mind that this testing does not mean you actually have to print these negatives on grade 2 paper when you set about making a fine print. It only means that their density ranges should approximately fit grade 2 paper.
Dont be surprised if less than half of your negatives fall into the on target category (i.e. print with good highlights on grade 2 paper). Remember, the object is to get a development time such that those negatives that dont print with good highlights on grade 2 paper are split more or less evenly between prints that have too dark highlights and too light highlights, but still fall within the extremes of Normal. If half your test prints are in the too light pile, and the other half in the too dark pile, with none in the correct pile (after youve eliminated those subjects that were incorrectly analyzed), youve still achieved a correct development time! The object is not to get the most negatives that print on grade 2 paper, but rather to center their density ranges around a grade 2 paper. At this point, you know you have a correct N development time.
Its fairly well agreed that the limit for Zone System expansion is approximately N+2 with ordinary medium-contrast B&W films. Even this is a bit optimistic considering that most modern B&W films can only produce N+1 or 12 (T-grain films seem to be able to handle N+2 fairly readily). As a result, I will only describe N+1 and N+2 calibrations:
Expansion produces a speed increase, and you must compensate. Adjust your film speed 2-stop higher for both N+1 and N+2 negatives (i.e. use the same speed for both classes of negative). Again, these are educated guesses for which more precise adjustments can be made later. Two words of caution First, you are not likely to get a genuine increase in speed that is significantly greater than 2-stop, no matter how long you develop film. Second, most legitimate increases in speed will take place while going from N to N+1 what appears to be further speed enhancement between N+1 and N+2 is almost certainly due to increased fog and very little, or not at all, to increased speed.
The next step is to find a starting development time for N+1 negatives. Since were using negative feedback, we can start anywhere. Naturally, a reasonable educated guess is in order. Most Zone System photographers end up using an N+1 time that is approximately a 30-percent increase over their normal time for conventional B&W films. With T-grain films, N+1 times are about 20-percent greater than normal times. (An even simpler approach is to use the manufacturers recommended Normal development time as your starting N+1 time.) This is certainly a logical place to start.
Shoot subjects analyzed as requiring N+1 treatment. Again, the more the better, because you will make mistakes. Use the 2-stop film speed adjustment, and bracket one full stop in 2-stop increments on either side for each subject, just as you did for N calibration. You will have five different exposures for each scene.footnote 3 Develop the film using the starting N+1 time you devised.
To determine a refined N+1 film speed and development time, follow the same procedure described previously for N film speed and development time determination.
For an N+2 expansion, start with the same film speed as for N+1 and increase development time by 50-percent over the N+1 time for regular films and by 30-percent for T-grain films. Follow the procedures already outlined to analyze speed and development.
Unlike expansion, there are a wide variety of techniques available for contraction and all produce different film speed and development time changes. Determining a starting film speed and development time for N-1 or N-2 contractions is dependent on the technique employed. When using the traditional method of simply cutting development time, you can expect a significant loss in film speed and drop in development time to achieve, for example, an N-2 contraction. However, if you use a Selective Latent Image Manipulation Technique (see Selective Latent Image Manipulation Techniques), plan for a small, or no loss of film speed and no change in development time at all. Each technique has different characteristics.
Fortunately, the variations between techniques dont present as big a problem as you may think. Having already tested for N and expansions, the Zone System newcomer will have acquired some experience at judging exposure and development. This will help in establishing a starting speed and development scheme for the contraction to be calibrated. Here I will discuss calibrating for contraction using the traditional technique of cutting development time.
Knowing you can expect a speed loss for contractions, simply guess the initial speed loss to be one stop for N-1 and 12 stops for N-2). You will have little chance of being more than 2-stop off. This is certainly close enough for a starting speed. The only contraction methods I know that never produce a speed loss (described in my articles on contraction) are post-development techniques that do not lend themselves to calibration.
Once a starting speed and development time have been established, correct speed and development of contraction negatives can then be determined by the same methods previously outlined for normal negatives first, by printing your bracketed exposures of N-1 subjects for best Zone III detail, and then evaluating prints from those negatives for speed and highlights, exactly as before.
N-2 contractions are of course handled the same way as just outlined. Use the starting film speed determined for N-2, and a starting development time that is 30-40% less than the time determined for N-1.footnote 4
This is the appropriate place for an important bit of advice.
Give serious consideration to aiming your contraction negatives at a grade 3 paper, rather than grade 2. Contraction negatives of all types most frequently print best on grade 3 or 4 paper, rather than grade 2. Doing this replaces local contrast that was lost, due to contracted development (see The Primacy of Local Contrast). Since we know in advance that most contraction negatives will be printed on grade 3 paper, it only makes sense to aim contraction negatives at that paper grade to begin with!
Once familiar with the basic concepts behind this approach to calibration, it quickly becomes apparent that it is very adaptable to the individual. There are a great many shortcuts you can take, especially after gaining experience, and a large number of variations. Each photographer should be able to invent personal methods.
One of the things you will find as you go through the process is that with subsequent calibrations, you can begin to skip a number of steps and also shoot fewer sets of test negatives.
When testing a new film or developer, an experienced Zone System photographer familiar with this approach to calibration may shoot four or five subjects, bracketing a halfstop on either side of the starting film speed, process the film for 2030% less than the manufacturers recommendation, then choose by visual inspection the negatives that appear to have received the best exposures. Those negatives might then be printed on a grade 2 paper for optimum shadow detail, and an altered development time chosen based on the appearance of the highlights in those prints. However, I want to caution you not to attempt to shorten the process to this degree until you are certain youre ready.
The most important points to remember when devising personal approaches to calibration are that each method must:
Always allow negative feedback to play a role.
You must go too far (i.e., have definite under- and overexposures and/or developments for comparison).
Sample a significant number of subjects so that wild cards can be eliminated, and so you can be certain of obtaining the correct average development or exposure for a number of shots of the same subject type.
Always assume that mistakes will be made and include that assumption in the design of your test methods.
First, last and always, make real photographs!