Lighting for High Speed

Lighting issues for high frame rate production are not specific to any one camera. Even with the great sensitivity of modern cameras, be prepared to use a considerable amount of light. When the frame rate is doubled the amount of light reaching the sensor for each frame is halved. This is equivalent to one “stop” of light on a lens iris (i.e., T2.8 v T4) or a doubling of shutter speed (ie. 1/60th v 1/120th or 180° v 90°). The scale is logarithmic so the light is halved with each doubling of frame rate: 24, 48, 96, 192, etc. Therefore 240fps would need 3¼ more stops of light to match the light level of 24fps. This can be achieved by opening up the lens aperture by 3.25 stops (see chart). In addition to illumination levels, the largest issue in high speed lighting is flicker. AC electrical power uses alternating cycles of current 50 or 60 times per second (depending on the country and its power system). This cycling of power can cause tungsten and quartz halogen lights to dim as the power cycles, resulting in flicker. This flicker is too fast to see with the naked eye or at traditional shooting speeds, but can be revealed at high frame rates. Frame rates at or double the power cycle rate generally do not show this flicker, so in 50hz regions there is no flicker at 50fps or 100fps and in 60hz countries there is no flicker at 60fps or 120fps. The amount of dimming is related to the type of bulb, wattage and physical size of the filament. In general, large quartz halogen fixtures of 2000w and above are so highly heated that they do not have time to cool and dim before the power cycles back up. DC powered tungsten and quartz halogen lights are always on and do not flicker. HMIs and fluorescents are generally okay for speeds at or below 120fps as long as they utilize modern electronic ballasts. Most LED fixtures use pulse-width modulation (PWM) to adjust brightness, meaning that the control circuits introduce pulsing of the lights at variable frequencies. Used at 100% brightness these and other professional video production LED fixtures should not flicker. Household and industrial LED lamps should be avoided. Remote Phosphor and plasma light fixtures designed for the motion picture industry cycle at extremely high frequencies and will not produce flicker.

Applies To

Odyssey7Q+, Odyssey7Q

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Created : 2016-04-29 21:44:34, Last Modified : 2016-04-29 22:24:39

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