135 Film (35mm Still Film / ISO 1007)
Direct Answer
135 Film (standardized under ISO 1007) is the most popular photographic film format in history, consisting of a 35.0 mm wide cellulose acetate or polyester strip with standard KS-1870 sprocket perforations housed in a light-tight metal cassette. Capturing standard 36 × 24 mm frames in 24 or 36 exposure lengths, it utilizes electrical DX-barcode contacts to auto-set ISO speed and exposure latitude.
Source: ISO 1007:2000 (Photography — 135-size film and magazine — Specifications) / ANSI PH1.14
Specs
| Film Strip Width | 35.00 ± 0.05 mm (1.378 in) |
| Nominal Image Frame Size | 36.0 × 24.0 mm (standard 3:2 aspect ratio) |
| Perforation Standard | KS-1870 (Kodak Standard) rectangular perforations (4.75 mm pitch along both edges) |
| Standard Exposures per Roll | 24 or 36 exposures (approx. 115 cm and 165 cm total strip lengths) |
| DX-Code Electrical Grid | 12-contact checkerboard grid on metal cassette (encodes ISO 25 to 5000, frame count, exposure latitude) |
| Spool Core Diameter | Standard 11.0 mm plastic center spool with slot tab for loading |
| Legendary Cameras | Leica M3/M6, Nikon F3/FM2, Canon AE-1, Olympus OM-1, Contax T2 |
The 12-Bit DX Encoding System
Introduced by Kodak in 1983, the DX (Digital Index) barcode uses exposed bare metal and painted insulating squares on the film canister. Electronic contact pins in modern 35mm cameras read this 12-bit grid to automatically program the camera's light meter to the film's exact ISO speed ($100, 200, 400, 800$), eliminating manual user ISO setting errors.