Nowell has been working in Hollywood since the 1970s. His first project was John Cassavettes' acclaimed 1974 drama A Woman Under the Influence, on which Nowell was a camera operator. Nowell then joined the tumultuous production of the acclaimed Vietnam War film Apocalypse Now, which featured Albert Hall and which won the 1978 Academy Award for Best Cinematography. Afterward, Nowell became an assistant aerial camera operator on the 1978 thriller Capricorn One, which featured music by Jerry Goldsmith and performances by David Huddleston and James B. Sikking. Other early aerial photography credits include The Great Santini (1979) and The Blues Brothers (1980, featuring Henry Gibson and Charles Napier).