Words from Rollei:

Rollei Ortho 25 is a technical, orthochromatic black and white photographic film with a nominal sensitivity of ISO 25/15 °.

Rollei ORTHO 25 is characterized by a high sensitivity reserve of up to two f-stops, depending upon development. The document emulsion offers exceptionally fine grain images with high sharpness. Rollei ORTHO 25 is ideal for technical and scientific applications and as a half-tone film for pictorial photography. The crystal-clear RC base opens up the possibility of using the film as a B&W slide film.

Technical and scientific applications:
• reproductions 
• reproduction of X-ray images 
• astrophotography 
• black and white slides and blue slides 
• graphic distancing For this application in particular, we recommend Rollei High Contrast (RHC) developer (1 5, 3 - 5 min.). Halftone film for pictorial photography: Rollei Ortho 25 in combination with Rollei Supergrain (RSG) fine grain contrast developer offers the highest standards of sharpness and extreme fine grain. Ortho 25 has also developed a legendary reputation when used in combination with Rollei Low Contrast developer. The results are reminiscent of qualities obtained by a Technical Pan film. The comparatively steep gradation is softened by this special developer. Extreme fine grain and high sharpness, coupled with detailed gray tones can be achieved in this way. Features: 
• low-speed orthochromatic black and white film 
• spectral sensitivity 380 to 610 nm 
• special coating to improve the transport properties of the film in the camera 
• suitable for use in daylight and artificial light, without any restrictions 
• polyester base with high tear resistance, suitable for archiving LE 500. Extremely high resolving power of 330 line pairs/mm, depending on the developer 
• very fine grain and high sharpness as a base for excellent-quality negatives 
• ideal for scanning and digital processing