ISO

Definition

ISO (International Organization for Standardization) is the light sensitivity of a camera sensor or film emulsion. The ISO value indicates how sensitive the recording medium is to light. A higher ISO value allows for shooting in lower light conditions, but typically leads to increased noise.

Historical Context

The ISO standard was established in 1974 as a merger of:

• ASA (American Standards Association): American standard since 1943
• DIN (Deutsches Institut für Normung): German standard since 1934
• ISO 100 corresponds to the former ASA 100 or DIN 21°

The ISO scale is logarithmic: each doubling of the ISO value corresponds to one stop of light gain.

Typical ISO Values in Practice

Film Emulsions

• ISO 50 - Kodak Vision3 50D (Daylight, very fine grain)
• ISO 200 - Kodak Vision3 200T (Tungsten, standard)
• ISO 500 - Kodak Vision3 500T (Tungsten, higher sensitivity)

Digital Cameras - Native ISO

• ISO 100-200 - Very low, maximum image quality, requires a lot of light
• ISO 400-800 - Standard for productions (RED, ARRI Alexa native 800)
• ISO 1600-3200 - Available light, acceptable noise
• ISO 6400+ - Extreme low-light, visible noise

Dual-Native ISO

Modern cameras like RED V-Raptor or ARRI Alexa 35 with two optimization points:

• RGB Primary ISO: 800 (ARRI) or 800/3200 (RED)
• Alternative ISO: 3200 (ARRI) with only slightly higher noise
• Transition: Both ISO values yield similar image quality

Noise Characteristics (Noise Profile)

Luma Noise

• Particularly visible in solid color areas (sky, walls)
• Increases exponentially with ISO
• Especially visible at ISO above 3200

Chroma Noise

• Less distracting than luma noise to the human eye
• Reddish or purplish spots in dark areas
• Can be treated in grading with chroma subsampling

Thermal Noise

• Occurs with long exposure times (over 1 second)
• Can be subtracted using dark frames
• Relevant for low-light cinematography

Practical Measurement and Calibration Techniques

Determining Native ISO

1. Perform white balance with an 18% gray card
2. Spot meter reading on gray card: target value typically EV 9
3. Combine manual ISO/aperture/shutter settings
4. Take a test shot and review in grading

ISO Exposure Index Differences

• EI (Exposure Index): Can deviate from native ISO
• Underexposure: EI 200 instead of ISO 400 (Reduction Factor 0.5) = +1 stop darker
• Overexposure: EI 1600 instead of ISO 800 (Pushing Factor 2.0) = +1 stop brighter
• Hybrid Approach: EI 1000 instead of ISO 800 = +0.33 stop (subtle adjustment)

ISO Strategies by Situation

Sunny Exterior Shoot (Daylight)

• Recommendation: ISO 100-400
• Typical Setting: f/5.6 at 1/48s and ISO 200
• Control Method: ND filters for aperture control

Interior Shoot with Practical Lights

• Recommendation: ISO 800-1600
• Typical Setting: f/4.0 at 1/48s and ISO 1200
• Equipment: Good base lighting ensures image quality

Low-Light Situation Without Artificial Light

• Recommendation: ISO 3200-6400
• Typical Setting: f/2.0 at 1/24s and ISO 4000
• Compromise: Noise is acceptable but visible

Night Shoot with Practical Lights

• Recommendation: ISO 3200
• Typical Setting: f/2.8 at 1/48s and ISO 3200
• Balance: Practical lights + native high ISO = optimal image quality

ISO and the Exposure Workflow

Expose to the Right (ETTR) with ISO

• At native ISO 800: maximum signal reserve
• Increasing ISO (instead of aperture/shutter): noise degrades linearly
• Decreasing ISO (instead of NDs): signal loss, weaker reserves

ISO and Log Codecs

• ARRI LogC: ISO 800 is optimal (0 dB), ISO 1600 is +6 dB gain
• Sony S-Log3: Native ISO 800, above 3200 with noticeable noise
• RED RAW: Noise minimally relevant, but processing-intensive

Errors and Solutions

Professional Best Practices

1. Prefer Native ISO: Best image quality and noise characteristics
2. Consistent ISO Throughout Shoot Day: Same look across all settings
3. Perform Test Shots: Test ISO in unknown lighting situations
4. Use Gray Card: 18% standard gray card for white balance and ISO consistency
5. Monitor Histogram: Check exposure and thus ISO performance

ISO Versus Related Concepts

Exposure Index (EI) vs. Native ISO

• Native ISO: Optimized gain level of the sensor
• Exposure Index: Actual exposure setting by the cinematographer
• EI can deviate from ISO for creative or practical reasons

Gain in Decibels (dB)

• 6 dB Gain: Doubling of light transmission (1 stop)
• 0 dB: Native ISO without additional gain
• +6 dB: ISO doubling
• +12 dB: ISO quadrupling

Historical Examples from Film History

• "Barry Lyndon" (1975): Stanley Kubrick used a Zeiss f/0.7 lens with low ISO for candlelight scenes
• "Goodfellas" (1990): Michael Ballhaus used ISO 320 on Kodak Vision 200T for a grainy look
• "Collateral" (2004): Thomson Viper at ISO 800 for nighttime LA streets
• "The Revenant" (2015): ARRI Alexa at ISO 800 for available light golden hour
• Netflix's "Mindhunter": ISO 3200 as standard for dark FBI interrogation rooms