Résumé
The globular cluster NGC 4833 lies near the galactic plane. It is known to exhibit a strong differential reddening caused by several galactic interstellar clouds in its line of sight. Based on two optical observation runs made in 2006 within and separated by a 6-month interval, we intend to detect the photometric variations (colors and magnitudes) of stars in NGC 4833 due to the varying interstellar reddening.