Color and thickness of soap films

The subject of soap films and their color is revisited. Following an educational path through wave optics, an account is provided for the color pattern of the films as related to the film thickness, spectral bandwidth of the light source, and sensitivity of the detector. A simple experimental setup is described, where a soap film is observed under illumination from an extended source and an image of the color pattern is recorded with a digital camera. The image data are analyzed to determine the thickness profile of the film, where the film thickness is obtained to within an accuracy of 3%. The data processing method is described, and examples of the determined film profiles are given. The presentation is suitable for students in their first years of college, but, if properly adapted, can also be appropriate for secondary school classes.