Ortho, short for orthochromatic, refers to a type of black-and-white film that is sensitive to all colours except red and deep orange. This unique spectral sensitivity allows the film to be handled safely under red safelights, making it convenient for darkroom work.
Orthochromatic films are typically high-contrast, producing strong tonal differences with few midtones. They are ideal for reproducing halftone images, graphic work, or artistic black-and-white photography where bold contrast is desired. Understanding ortho film helps photographers achieve precise tonal effects and maintain control over exposure and development.