ISO Speed Standards vs. Cinema Shutter Angle & 180° Rule
Comparing 2 standards across 11 specifications. 11 key differences identified.
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).
Shutter Angle (measured in degrees from 0° to 360°, originating from circular rotary disc shutters in 35mm motion picture cameras) is the cinematic standard for measuring exposure time relative to frame rate (Shutter Speed = Frame Rate × 360° / Shutter Angle). The universal '180-Degree Shutter Rule' (exposure time = 1 / (2 × Frame Rate)) delivers natural, organic motion blur that mimics human eye persistence.
Specification Comparison Table
11 Parameters| Parameter / Spec | ||
|---|---|---|
|
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) | — |
|
Mathematical Formula
|
— | Shutter Speed (t) = 1 / (Frame Rate × (360° / Shutter Angle)) |
|
180° Standard Shutter Rule
|
— | Exposure time is exactly half of the frame duration: at 24 fps = 1/48 sec | at 30 fps = 1/60 sec | at 60 fps = 1/120 sec | at 120 fps = 1/240 sec |
|
90° Narrow Shutter (Action Effect)
|
— | Fast exposure (1/96 sec at 24 fps) — crisp, staccato, jittery combat motion (Saving Private Ryan effect) |
|
360° Open Shutter (Dream / Smear)
|
— | Full-duration exposure (1/24 sec at 24 fps) — extreme motion blur, dreamy light trails, maximum low-light intake |
|
172.8° Shutter Angle (Flicker Reduction)
|
— | Eliminates 50 Hz European AC electrical lighting flicker when shooting at 24 fps in PAL regions |
|
Cinema Camera Standard
|
— | ARRI Alexa, RED, Sony FX6/FX9, Canon C300, and Blackmagic display shutter in degrees to maintain constant motion blur during frame rate ramps |