4a. In the Dark - Development
Development: The following is NOT a primer on the processing steps and chemicals required to develop film - if you are seeking that sort of information please refer to the "getting started" articles on Ilford's website. Rather this page is about understanding and fine-tuning those processes for optimal results. (Although as an aside and because this is where you might expect to find this information - even though it has already been discussed here, my developer of choice is Agfa Rodinal at a dilution of 1 part Rodinal to 50 parts water. Nice and sharp, lovely tones and grain isn't an issue when using 4x5 sheet film.) Now, on with what I really wanted to talk about...
We've already seen how film is exposed in accordance with the tenets of Ansel Adams' zone system, a system that provides a framework to formalise the first half of the old photographic rule: "expose for the shadows, develop for the highlights". I now want to turn to the second half of that rule.
In addition to exposure, B&W film users are fortunate to have a second important way of controlling how the tones of the scene are rendered on film, namely development. However, the impact of development is not even across all the tones. Varying the degree of development has less affect on the lower (darker) values, and a proportionately greater impact on the higher (lighter) values. More development will bump up the higher tones while the lower tones remain relatively unchanged. That is, it will increase the contrast of the image. For example, increased development might move a Zone VII tone to Zone VIII, while leaving the Zone III tones unchanged. Conversely, decreased development might move a Zone VII tone down to Zone VI while leaving Zone III tones unchanged.
We can take advantage of this feature to optimise the match between the subject brightness range ("SBR") of the scene and the film's ability to render those tones appropriately. When discussing exposure we said that after determining the correct exposure, the last step was to record the SBR of the scene, with a range of 5 zones (f-stops) between shadow and highlight being considered "normal", more than 5 zones being considered "contrasty", and less than 5 zones being "flat". We use that information to determine the amount of development to give to the particular image. A scene with a SBR of five zones will be given "normal" development, and the zones between Zone III and VII will be rendered faithfully on the negative. But a scene with a SBR of six zones will be given "reduced" development. This will drop the Zone VIII tones back to Zone VII while leaving Zone III tones unchanged. The zone system terminology for this is "contraction" because the tonal range of the scene is compressed to better fit the film's characteristics. Conversely, a scene with a SBR of four zones will be given increased development thereby lifting the Zone VI tones to Zone VII. This is called "expansion".
The objective is to develop the film so that the lightest values that are to retain information are rendered on Zone VII (while retaining the shadow detail on Zone III). Hence the second part of the rule: "...develop for the highlights." The SBR - and in particular the value of the highlights relative to the Zone III shadows - determines the degree of development given to the film: normal, contracted or expanded.
A couple of things to note:
Concluding Remarks: exposure and development are closely related - they can be seen as two sides of the same coin. If you are interested in finding out more and doing some elementary testing then, in addition to Ansel Adams' book "The Negative", I also recommend the following article: "Use Your Eyes!" by Paul Wainwright. It will help with the three related aspects of finding your film speed, appropriate exposure and development.
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