ISO Speed Standards
Exposure & Optics · 5 specs
Direct Answer
ISO Speed (standardized under ISO 12232 for digital sensors and ISO 6 / ISO 2240 for film, combining historical American ASA arithmetic and German DIN logarithmic scales) defines the sensitivity of an imaging medium to light. Operating on an arithmetic doubling progression (ISO 100 -> 200 -> 400 -> 800 -> 1600 -> 3200 -> 6400), each step doubles sensitivity, requiring half the exposure time (+1 EV).
Source: ISO 12232:2019 (Photography — Digital still cameras — Determination of exposure index, ISO speed ratings, standard output sensitivity) · Last reviewed Aug 28, 2026
Specs
| Standard Arithmetic Progression | ISO 50 -> 100 -> 200 -> 400 -> 800 -> 1600 -> 3200 -> 6400 -> 12800 -> 25600 -> 51200 -> 102400 |
| 1/3-Stop Increments | ISO 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200 |
| Dual Native ISO Architecture | Two distinct analog gain circuits, switched rather than blended (e.g. Sony A7S III/FX3 in S-Log3: Low Base ISO 640 / High Base ISO 12,800 -- exact pair varies by camera and picture profile) |
| Base ISO Signal-to-Noise | Maximum dynamic range and 14+ stops of tonal latitude typically occurs at the camera's lowest native hardware ISO (e.g. ISO 100 or ISO 64 on Nikon D850/Z8) -- dual native ISO sensors are the exception, with a second local peak at their high base ISO |
| Historical Standard Fusion | ISO 400/27° fused American ASA 400 (arithmetic) with German DIN 27° (logarithmic) |
Dual Native ISO Circuitry
Traditional digital sensors apply digital amplifier voltage to boost low-light signals, amplifying noise floor voltage. Dual Native ISO sensors incorporate two separate physical analog readout circuits per pixel: at high ISO thresholds (e.g. ISO 3200 or 12800), the sensor switches to a low-noise high-conversion-gain circuit, instantly resetting dynamic range and eliminating shadow noise.