Several variables influence proper exposure.
Knowing them is the key to capturing what you want on film. In the years that I have been teaching photography, I have found exposure to be one of the easiest or hardest aspects of photography depending upon whether the photographer is more left or right brain developed. While at first this might sound reasonable, what is familiar and realistic to some may not be to others. With the extreme variations in color printing it never ceases to amaze me how some photographers can claim that the colors of a sunset shot two weeks before are exactly the same as on a 4x6 print just received from their favorite commercial photofinisher. This is a relatively normal phenomenon however and this 4x6 can serve as an acceptable guide for any subsequent reprints or enlargements.