Abstract: An electrostatographic recording apparatus includes an endless recording member upon which toner images are recorded. A densitometer is provided for measuring density of a toned area on the recording member. The densitometer includes a light emitting and/or light sensitive component that is located in an internal space confined by the endless recording member. The densitometer further includes a slidable support upon which the component is mounted in facing relationship with and proximate to an internal facing portion of the recording member. A stationary mounting structure is attached to a film core upon which the film-like recording member is supported. The slidable support is received within the stationary mounting structure. An electrical circuit is electrically connected to the component and is mounted on a side of the slidable support that is opposite in facing direction to that of the component.