American musician and photographic technician known as a codeveloper of Kodachrome film (1935).

Mannes attended New York City's Riverdale School, where he met his future partner, Leopold Godowsky (Godowsky, Leopold, Jr.), Jr. They enjoyed a mutual interest in music and photography, and together they set up a small laboratory for experimentation with colour film. In 1917 Mannes went to Harvard University to study physics and musicology. After receiving his B.A. in music, he taught at the Mannes School of Music in New York City, an institution founded by his parents. Mannes continued his research in photography, however, and collaborated with Godowsky by mail.

In 1919 Mannes and Godowsky created a mediocre colour film, at which time they realized that the additive process they had been working with would not give them the true colours that they sought. It was at this point that Mannes and Godowsky switched to a multiple-layered subtractive-film approach that would eventually lead them to the development of Kodachrome. They opened their first real laboratory in New York City in 1922, and with the backing of Dr. C.E. Kenneth Mees of the Eastman Kodak Company in 1930, the duo moved to Rochester, N.Y., to work with assistants at the well-equipped Kodak Research Laboratories. On April 15, 1935, Kodachrome's development was announced as the earliest of the colour-subtractive films that proved a boon to colour photography. Though originally used for animated motion pictures, Kodachrome was later improved, and it remains a popular film today. Mannes returned to the Mannes School of Music, which he renamed the Mannes College of Music in 1953 after he became director, a position he held until his death.