Short and Long Exposure Time-lapse
As mentioned above, in addition to modifying the speed of the camera, it is important to consider the relationship between the frame interval and the exposure time. This relationship controls the amount of motion blur present in each frame and is, in principle, exactly the same as adjusting the shutter angle on a movie camera. This is known as "dragging the shutter".
A film camera normally records images at twenty four frames per second. During each 1/24th of a second, the film is actually exposed to light for roughly half the time. The rest of the time, it is hidden behind the shutter. Thus exposure time for motion picture film is normally calculated to be one 48th of a second (1/48 second, often rounded to 1/50 second). Adjusting the shutter angle on a film camera (if its design allows), can add or reduce the amount of motion blur by changing the amount of time that the film frame is actually exposed to light.
In time-lapse photography, the camera records images at a specific slow interval such as one frame every thirty seconds (1/30 frame/s). The shutter will be open for some portion of that time. In short exposure time-lapse the film is exposed to light for a normal exposure time over an abnormal frame interval. For example, the camera will be set up to expose a frame for 1/50th of a second every 30 seconds. Such a setup will create the effect of an extremely tight shutter angle giving the resulting film a stop-animation or claymation quality.
In long exposure time-lapse, the exposure time will approximate the effects of a normal shutter angle. Normally, this means the exposure time should be half of the frame interval. Thus a 30‑second frame interval should be accompanied by a 15‑second exposure time to simulate a normal shutter. The resulting film will appear smooth.
The exposure time can be calculated based on the desired shutter angle effect and the frame interval with the equation:
Long exposure time-lapse is less common because it is often difficult to properly expose film at such a long period, especially in daylight situations. A film frame that is exposed for 15 seconds will receive 750 times more light than its 1/50th of a second counterpart. (Thus it will be more than 9 stops over normal exposure.) A scientific grade neutral density filter can be used to compensate for the over-exposure.
Read more about this topic: Time-lapse Photography
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