He developed the “zone system”, which consisted of 11 shades of gray, and could manipulate exposure and development to a point where he could control what zone a particular object would appear. Getting details in both the shadow and highlight areas in a photo is made much simpler using the zone system. In addition to that, his work in documenting the national parks, Yosemite in particular, was instrumental in developing interest in the national park system.
Ansel Adams style was based on visualization of the final image prior to exposure and through the development process and printing process to achieve that visualization. Is images are rich in tonal quality from rich deep blacks,to creamy midtones, to bright whites that maintain detail. Many of his prints are also selenium toned, this process deepened the blacks altered the overall print to provide a warmer image.
Ansel Adams was also a maestro in printing in the darkroom. He often times referred to the negative as the score and the print as the performance of that score. Through expert burning and dodging techniques, he could achieve in the final print and emotion conveyed through his “mind’s eye” to the viewer.