A device for transilluminating a film has a light exit emitting with a light beam for transilluminating the film, a transillumination region for guiding the film such that the light beam can transilluminate the film in the transillumination region, a film feed for feeding the film to the transillumination region and a film removal for removing the film from the transillumination region. The device moreover includes a hollow chamber with a diffusely reflecting inner surface and a light entrance opening receiving light from a light source and an exit opening, as well as an optical guide having a beam entrance end and a beam exit end. The beam entrance end is arranged such that light exiting from the exit opening of the hollow chamber at least partially enters through the beam entrance end into the optical guide.