Doug Kerr
Well-known member
It is very common for the "sensitivity" of dedicated video cameras to be stated in terms of the minimum scene illuminance (ambient lighting) under which they can deliver a "usable" image, and to state that illuminance in the SI unit, lux.
I thought it would be interesting to compare this with the terms in which we commonly think in the still camera world.
A common rating for dedicated video cameras is 0.5 lux. In APEX terms, this corresponds to Iv -7.1. This is said to be about the illuminance afforded by the light of the full moon under good conditions. My incident light exposure meter provides scale markings down to 0.125 lux, with good readability down to 0.5 lux.
Under the "standard exposure equation" with scene luminance known (often described as the "incident light metering" form of the equation), for a camera sensitivity of ISO 400, this scene luminance would call for a photographic exposure of EV -0.1 (about f/2.0 at 2 sec).
By way of comparison, an exposure of 1/30 sec with an aperture of f/2.8 is Ev 7.9.
Thus, it would seem, a dedicated video camera with a rated sensitivity of a scene illuminance of 0.5 lux would seem to be 8 stops more sensitive that a still camera at ISO 400, 1/30 sec, and f/2.8.
Lest my math have gone wrong, or my favorite exposure calculator, I had my light meter do the same reckoning, with the same result.
I am startled by this result.
To take a properly exposed still picture with a scene illuminance of 0.5 lux (assuming the normal range of scene item reflectance) would seem to require perhaps this setup:
ISO 3200, f/2.0, 1/2 second.
How can this be?
Best regards,
Doug
I thought it would be interesting to compare this with the terms in which we commonly think in the still camera world.
A common rating for dedicated video cameras is 0.5 lux. In APEX terms, this corresponds to Iv -7.1. This is said to be about the illuminance afforded by the light of the full moon under good conditions. My incident light exposure meter provides scale markings down to 0.125 lux, with good readability down to 0.5 lux.
Under the "standard exposure equation" with scene luminance known (often described as the "incident light metering" form of the equation), for a camera sensitivity of ISO 400, this scene luminance would call for a photographic exposure of EV -0.1 (about f/2.0 at 2 sec).
By way of comparison, an exposure of 1/30 sec with an aperture of f/2.8 is Ev 7.9.
Thus, it would seem, a dedicated video camera with a rated sensitivity of a scene illuminance of 0.5 lux would seem to be 8 stops more sensitive that a still camera at ISO 400, 1/30 sec, and f/2.8.
Lest my math have gone wrong, or my favorite exposure calculator, I had my light meter do the same reckoning, with the same result.
I am startled by this result.
To take a properly exposed still picture with a scene illuminance of 0.5 lux (assuming the normal range of scene item reflectance) would seem to require perhaps this setup:
ISO 3200, f/2.0, 1/2 second.
How can this be?
Best regards,
Doug
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