Antihalation protection

Photographic material always has a light-sensitive emulsion and a base, the so-called carrier material. When the material is exposed, however, the negative effect occurs that either the light is reflected on the substrate or the pressure plate behind it and thus causes reflections in the image ( reflection halo ), or the light is lost in the layer and leads too blurring (diffusion halo).

A halo protection is created especially for the case of reflection halos; it is ineffective in the case of diffusion halos. An antihalation layer is poured onto the back of the film or plate, which attenuates such reflections. In the case of 35mm and cinema films, however, the antihalation layer is applied between the emulsion and the carrier material. This is due to the much greater mechanical stress on its back. Historically, therefore, such halo layers were first used in roll films and photo plates .

Such halo layers, also called antihalo layers or AHU, have a very beneficial effect. While it is hardly possible with unprotected materials to depict bright, sunlit surfaces (e.g. streets, blond hair) without sharpness-reducing overexposure, it is possible to overcome even the highest contrasts with good atrial protection.