Exposure Value (EV) vs. T-Stop
Comparing 2 standards across 10 specifications. 10 key differences identified.
Exposure Value (EV, standardized under ISO 2720) is a logarithmic base-2 scale quantifying combinations of shutter speed and relative aperture that yield identical photographic exposures (EV = log_2(N² / t) at ISO 100). Governs light metering, auto-exposure compensation, dynamic range benchmarks, and the classic 'Sunny 16' outdoor rule.
The T-Stop (Transmission Stop, standardized under ISO 517 for cinematography) is a photometric measurement of a lens's true light transmission (T = f / √Transmittance), correcting the theoretical geometric f-stop for physical light lost to glass reflection and optical element absorption. Standardized across all cine primes (Cooke, ARRI, Zeiss, Angénieux).
Specification Comparison Table
10 Parameters| Parameter / Spec | ||
|---|---|---|
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Mathematical Formula
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EV = log₂(N² / t) — where N is f-number and t is shutter speed in seconds (at ISO 100) | T-Number = F-Number / √(Transmittance Percentage as a decimal) |
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EV 0 Baseline
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Aperture f/1.0 with a 1.0-second shutter speed at ISO 100 | — |
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Sunny 16 Rule (EV 15)
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Bright direct outdoor sunlight = EV 15 (Set aperture to f/16, shutter speed = 1 / ISO speed, e.g. 1/100s at ISO 100) | — |
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Typical Real-World EV Benchmarks
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EV -4: Full moon night sky | EV 4: Candlelight interior | EV 7: Typical home interior | EV 12: Overcast day | EV 15: Sunny beach/snow | — |
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Auto-Focus Low-Light Rating
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Modern mirrorless AF sensitivity is rated down to EV -6 to EV -9 (operational in near pitch-black darkness) | — |
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Dynamic Range Measurement
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Expressed in EV stops (e.g. 14 EV of sensor dynamic range = a 16,384:1 contrast ratio) | — |
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Physical Meaning
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— | A lens set to T2.8 transmits the exact same photometric illumination to the sensor as an ideal 100% transparent lens at f/2.8 |
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Complex Zoom Glass Loss
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— | A 18-element zoom marked f/2.8 with 80% transmission has an actual transmission rating of T3.1 (0.3 stops darker than f/2.8) |
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Cinema Iris Ring Markings
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— | Marked strictly in T-stops with linear mechanical spacing and clickless 0.8 MOD gears for follow focus rigs |
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Shot-to-Shot Matching
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— | Switching from a 24mm wide lens to a 85mm telephoto on a movie set, both set to T2.8, is designed to hold exposure and luminance effectively constant across the cut |