Since meters in general average a given scene, the big compromise is that most scenes are not average. While the exposure may be OK, it can probably be better. There are several things that can help make this happen. They require some testing, and some careful observation, but are worth it.
Some things to keep in mind are first, that meters do average, and what they average for is middle grey. Second, that ASA/ISO ratings and film development times are really recommendations, and your results may vary. The variance can be caused by many factors: the meter itself, how you process the film (such as how it is agitated), the camera shutter's accuracy, the thermometer that you use. Because of these variations, consistency is very important. Third, different film/developer combinations will give different results.
Because of the above, using a single film/developer combination, and being very consistent with processing, allows you to observe and make reasonable judgements on what is happening with the negative. Exposure controls density. Consistently thin negatives can be caused by a meter that reads too high or a shutter that operates too fast. This can be corrected by using a lower ASA/ISO. Consistently dense negatives can be corrected by using a higher ASA/ISO.
Development controls contrast, while exposure controls density. the saying is "Expose for the shadows, develop for the highlights". Consistently flat negatives can be corrected by either increasing the development time, or reducing the development dilution. Consistently contrasty negatives can be corrected by the opposite: reduced development time or increasing the developer dilution. Both of these can be tested, to get more accurate, empirical data. Again, the tests are for a single film/developer combination.
The Zone System may seem quite intimidating to a beginner, but it simplifies talking about tonality by breaking it down into distinctive levels, or zones. The system uses either nine or ten zones (depending on the particular source). With ten zones, values are numbered from 0 to IX. (The zone numbers are universally capital roman numerals).
Each zone represents a one-stop difference in tone. The zones refer to both paper and print values, with the density reversed from one to the other. So Zone 0 for paper defines maximum density, the maximum black the paper can produce, while on the negative it is no density, or clear.
|0||Maximum black a paper can produce. For film, it is the film base plus fog, or the most transparent part of the film.|
|I||Nearly as black as 0 on paper. Usually the only way to tell the difference is a side-by-side comparison. Same on film. A slight density change over 0, but no texture or detail.|
|II||Slightly textured black on paper. The first indication of anything but a void. Usually what actually black objects should be printed at.|
|III||A very key zone, III defines dark with detail. The darkest areas where detail and texture is fully defined. The easiest place to see Zone III is shadowed foliage.|
|IV||Light shadow, dark skin.|
|V||The second key zone, Zone V is middle or neutral grey, defined as 18% reflectance. This is the tone meters read for. Grass in light, weathered wood.|
|VI||Sounds odd, but Zone VI is a dark highlight. Caucasian skin in light. Bare concrete in bright sunlight.|
|VII||The third key zone, Zone VII is white with detail. The brightest area that shows full detail and texture. Zone VII defines significant highlights.|
|VIII||The last highlight area that shows texture. Well-lit white objects, highlights that should have texture are rendered in Zone VIII.|
|IX||A highlight with just a hint of tone. The light companion to Zone I. Zone IX is often what is sought at the frame edge with a bright sky. Just a hint of tone to define the edge.|
|X||Full paper white, maximum film density.|
The zones are often divided into dark, or black, Zones 0-II, textured, Zones II-VII, and bright or white, Zones VII-X. The majority of most images should fall in the textured zones, with the blacks and whites providing contrast.
Becoming fluent with what values zones represent will make looking at and judging images more objective. Not all images require all zones, but most will. Spreading the tones of an image across more zones makes for an image that becomes more interesting to look at, luminous rather than flat or contrasty.
Previsualization refers to a technique of envisioning how a scene will look as a print, before it is even recorded on film. It involves examining a scene and deciding or determining what a particular value should look like, what zone it represents. This gives you the beginning of a plan on how to approach the subject, first with the exposure, then through processing the film and printing the image.
Placement uses careful metering to ensure shadow detail. Exposure controls the density of the film. This becomes readily apparent when looking a the thin shadow areas. You cannot print what is not there, so those shadow areas require a reasonable amount of detail, or they become dead zones in the print.
Dark with detail, the darkest zone with full detail, is Zone III. This is two stops less than Zone V, or medium grey, which is what your meter meters for. To ensure proper detail, we place the significant shadows of a scene into Zone III. To do this, you meter the shadow area only. Fill the viewfinder. You can additionally throw the image way out of focus, which will even out the values more. Take a meter reading. Set your exposure for two stops less than that reading, recompose, and take the exposure. You significant shadows should now have Zone III density when processed.
Film Speed (ASA/ISO) Test
There are very detailed methods for test your film speed, as detailed in Chris Johnson's The Practical Zone System or Lambrecht and Woodhouse's Way Beyond Monochrome. It is relatively easy to do a version of the test that does not require a massive amount of work.
The general procedure is to make a series of exposures of an easily readable scene, using the ASA/ISO setting to bracket. Then make a series of prints from these negatives, all using the same enlarger settings (see Paper Black Test below), then evaluate the results.
Carefully meter a scene that has a wide variety of tones, especially shadow areas and highlights with detail. Look for an average scene, not too contrasty, not too flat. To start with, use the recommended ASA/ISO for the film you are using. Take several blank frames (just keep the lens cap on). Then make an exposure at the recommended, metered setting. From here, there a couple of ways to go. Lambrecht and Woodhouse's Way Beyond Monochrome uses the ISO setting to increase exposure by 1/3 stop for five frames. As an example, with 400 ISO film, the first frame would be at 400. Next at 320, then 250, 200, 160, and finally 125. This will give you a series of exposures, each increasing by 1/3 stop. They then recommend developing the film at 15% less time than normal.
Johnson's The Practical Zone System uses the following sequence:
|Frame 1||Normal exposure, standard ISO|
|Frame 2||1/2 stop less than 1|
|Frame 3||1 full stop less than 1|
|Frame 4||1 1/2 stops less than 1|
|Frame 5||2 stops less than 1|
|Frame 6||Same as 1|
|Frame 7||1/2 stop more than 1|
|Frame 8||1 full stop more than 1|
|Frame 9||1 1/2 stops more than 1|
|Frame 10||2 stops more than 1|
|Frame 11||Blank frame|
Johnson also recommends using normal (recommended) development.
Once the film is developed and dried, the next step is to make prints of the images. These will all be printed at the same exposure, the Standard Print Time.
Paper Black, Standard Print Time Test
Start by determining the paper black, or standard printing time. This is the minimum amount of exposure the paper needs, at a particular enlargement, to reach black. Cut a section of blank film in half, and place it in the negative carrier in the enlarger so that it only covers half the frame. Set your enlarger height to make a normal-sized enlargement for the size paper you are using.
Close the enlarger down at least two stops (f/11?). Make a standard test strip (see printing), and carefully process the paper.
Let it dry completely, and evaluate. You should have at least two exposures where the open and the film base side are black, or nearly so. The lighter (shorter time) of the two will be your standard printing time. It is the least amount of time needed to produce black through the film base, at that enlarger height and that enlarger aperture. You will use these settings for the rest of the test.
Keeping the enlarger settings the same, make a print of each frame from the test using your standard printing time. Mark each one, so that you know which frame they are form.Once the prints are dry, the evaluation begins.
What you are looking for is the fastest ASA/ISO setting that gives good detail in the shadows. This will become your effective speed for that film. In most cases, it will be up to a stop more than recommended (a lower ISO value).
Development controls contrast by controlling the density of the highlight areas. Examining the chosen print from above will give evidence on what to do with development. If the highlights are grey, the development needs to be increased. If they are blown out, or completely white, the development needs to be decreased.Testing this to get definite, empirical results is required to determine how much the development time should be altered.
Again, using the method described in Lambrecht and Woodhouse's Way Beyond Monochrome, you will expose two rolls of film. Choose a scene (or scenes) with both significant shadow and highlight detail. Using the tested ASA setting for the film, expose both rolls. Cut the first roll in half, and load it into separate tanks, or load one half and place the other in a light-tight container. Develop this first half at the recommend time for the developer you are using. Develop the second half for 15% less time.
When the film is dry, make a standard print from each. Examine the highlight detail in the print. If either produces good detail, that is your standard developing time. If both produce blown highlights, develop half of the second roll for 30% less time. If the first two produce flat or muddy highlights, increase the time on the first half of the second roll by 20%. Still flat, go to 40% more time.
The combination of testing the film speed and development times will go a long ways towards getting negatives that are much easier to print.
Expanding and Contracting Development
While exposure controls density, development can be used to control contrast. This happens by manipulating the highlight density. While the shadows are fully developed fairly early in the development process, the highlights, the densest areas on the film, continue to get denser as development continues, until they are at maximum density. So, if the scene is very contrasty, using a shorter development time, or contracting development, will keep the highlights from becoming too dense. Likewise, with a flat scene, contrast can be increased by expanding, or lengthening the development time.
With black and white film, the viable amount of expansion and contraction is two stops either way. More than that risks, on the contraction side, underdeveloped middle tones, and on the expansion side, fogging the shadows.
The development times are based on the standard time, which should be based on testing, but can be based on manufacturer's recommendation. This becomes Normal, or N.
|N-1 (one stop contraction)||70% of Normal|
|N-2 (two stops contraction)||60% of Normal|
|N+1 (one stop expansion)||140% of Normal|
|N+2 (two stops expansion)||140% of N+1|
|N-1||90% of Normal|
|N-2||80% of Normal|
|N+1||110% of Normal|
|N+2||110% of N+1|
Successful altering of the development time depends on careful metering of both significant shadow and highlight areas, and calculating the difference, in stops. Ideally, the significant shadows are placed in Zone III, with the significant highlights falling in Zone VII, a five Zone, or stop, range. If the range is six stops, then the scene is contrasty, and would require N-1 development. If the range is, say three stops, then we apply N+2 development.
*** Example ***
The Zone System In Practice
- 1. Previsualize. Examine the scene and determine the placement of the important shadow detail. This will usually be into Zone III.
- 2. Carefully meter that shadow area. Fill the viewfinder. Note this reading, as it is what your exposure will be based on.
- 3. Meter the significant highlights, and make a note of the reading.
- 4. Calculate the exposure. To place the shadows in Zone III, the exposure should be set for two stops less than the metered exposure. Compose the image and make the exposure.
- 5. Calculate the difference in stops between the shadow reading and the highlight reading. This will determine how the film is processed, Normal, Normal+, or Normal-.