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by lcrs
4369 days ago
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Even cameras which vary speed during an unbroken shot automatically compensate so the exposure stays the same, but doing so has other interesting effects, depending how it's done: a) Compensating with shutter so that the integration time is constant means the quality of motion blur changes during the ramp. For example a shot that starts at 24fps and ramps to 120fps keeping a shutter time of 1/240th would start out with really crisp-looking "skinny shutter" motion, and you might see flickering and strobing if there's much camera motion. The end of the ramp would have normal looking amounts of motion blur. If there are CRTs or fluorescent lights in shot they'd flicker at different rates throughout the ramp. It can be a dead giveaway that something's about to happen if a shot starts with really tight motion blur like that. b) Compensating with lens aperture is much less common because the depth of field changes, but starting with everything in focus, the focus becomes much tighter with the background way out of focus at high speed. Reportedly, mechanical problems tend to manifest as the aperture overshooting its mark or bouncing back leading to brightness variations at the end of the ramp. c) Compensating with ISO/gain is possible these days, which would avoid the above problems but would end up with a noisier image for the high-speed end. Recent bullet time shots are either fully CG, shot with an array of cameras, or cheated by hanging everything on wires, but it's interesting to check if any of these things from the days of 16mm skate films with the classic hang-time dips are re-created :) |
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