Ansel Adam’s ‘Zone System’ is something that all photographers have to be aware of
To put it simply, any scene is divided in brightness from 0-9 (IX), with zero being pure black and IX being pure white with no details .. and zone V the middle neutral grey 18% which the camera metering always aims for .. with each zone or stop double the one below in brightness or vice versa ..
Although originally developed to understand and control the processing of black & white negatives and prints , it is still as relevant to the digital process as ever ..
Understanding this system helps setting the right exposure either in manual mode or by setting EV in program mode and also proper RAW processing in software ..
It is such an important cornerstone in photography that many books and articles were written about it .. and here are some nice comprehensive links about the subject:
, and I am sure any Google search would produce tons of results .. so happy researching and hopefully applying ..