Ansel Adams zone system is NOT a darkroom technique at all!
The zone system is a guide to set the right exposure based on spot ligth metering! I do use a zone system but actually I developed myself without knowing Ansel Adams' technique. For long time I also believed the zone system is a darkroom technique. Then I read about it and I found out I use the same thing, and it is not a darkroom tecnique.
The pull processing what Ansel Adams used for bring out more detail in a shadow area, is also not a post manipulation! The pull processing is actually must have to decided before the shot is taken!
The point of the technic is the folowing:
Those light sensitive particles wich not get enough lights are not react with the developer chemical and wash off from the surface of the film during the processing. During the enlargement process, when the negative projected to the photopaper, there is no any particle on the path of the light in the shadow area, so there is not gonna be any detail on the print!
But if we overexposed the film, even in a shadow area enough lights can be hit the film so during the processing the light sensitive particles react with the developer chemical and remains in the surface of the film. But because the film was over exposed (in purpose!) need a shoret developing time to corect it. But even the shorter developing time (pull processing) the particles remains in the shadow area too! That bring more details on a print. This technique works only using negatives!
On roll film, if one picture was over exposed in purpose for using a pull technique, all the others must overexposed too with a same EV!
Because this technique must be decided even before the shoot, it can't be called manipulations, or cheating.
I use push technique for getting higher contrast. It is mean I underexposed all my picture on a roll in purpose, with a same EV value, and it is corrected with the processing. If I accidentaly under or over exposed a frame that is became dark or bright! It is impossible to fix on a slide or negatives an accidentally wrong exposure! You can fix it on a print if it is not too much.
