During the sixties, Francine moved to New York where she became enchanted by the jazz scene and started experimenting with her technique, holding the shot and then moving the camera, as in a dance with the artist, to capture the emotion of the moment and the artist's movement. She created a blurred free-form still which had no stillness and mirrored the dynamic improvisation of the performer. She coined it "Fever" technique. This technique became iconic and has been imitated since by photographers around the world, on jazz record covers and magazines.

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Here are some examples of both high and mild fever.