Abstract: A device for measuring light scattered by an information support in which a light source is used to expose a portion of the information support. A sensor having a light-sensitive surface and an output signal dependent upon the quantity of light falling on such surface is positioned behind an objective lens disposed between the information support and the sensor. The exposed portion of the information support is smaller than the field of view of the sensor and the sensor is disposed at a distance behind the objective lens where the quantity of light on the light-sensitive surface of the sensor remains constant to within 5% in the event of a variation of .+-.20% in the distance of the information support from the objective. The light-sensitive surface of the sensor is disposed within the beam of light scattered by the information support and emerging from the objective lens.