ISO Speed Standards (ISO 12232 / ASA & DIN)
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)
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 capacitor gain circuits built into each pixel (e.g. Base ISO 800 and High Base ISO 3200 on Sony FX3/A7S III/Venice) |
| Base ISO Signal-to-Noise | Maximum dynamic range and 14+ stops of tonal latitude occurs strictly at the camera's lowest native hardware ISO (typically ISO 100 or ISO 64 on Nikon D850/Z8) |
| 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.