Topic:	Time Lapse flicker with Digital Single Lens Reflex (DSLR) cameras
Author/Copyright:	John Jovic

Flicker is common problem in time lapse and stop motion animation and is seen as minor variations in the exposure between adjacent frames in a sequence. These variations may in fact be quite minor but they become apparent and distracting when the images are viewed in quick succession such as in a time lapse video. Time lapse is often shot with Digital Single Lens Reflex (DSLR) cameras which can be prone to causing flicker as many of these cameras are simply not designed for this application.

There are many reasons for such exposure variations and the table below looks at some of the factors that can cause exposure variations, resulting in flicker, and looks at some of the steps that can be taken to improve the outcome.

For example, if a camera is used in Auto exposure, either Aperture, Shutter priority or Program modes, then the inconsistencies can be caused by the camera's metering system and the way it interprets the scene itself, or simply due to actual variations in the scene brightness. Another possible cause for exposure inconsistencies is because a DSLR light meter usually operates in 1/3 or 1/2 stop increments which are not fine enough for time lapse. These common causes of flicker can be avoided altogether by shooting with manual exposure settings when ever possible. Unfortunately flicker often occurs even when manual settings are used. This can be due to a number of mechanical reasons such as inconsistencies in the actual aperture or shutter speed achieved during the exposure compared to the desired or intended aperture or shutter speed which have been set on the camera or lens. It seems that some cameras and lenses are incapable of accurately reproducing the exact same aperture or shutter speed from exposure to exposure. These inaccuracies are quite minor and can have greater or lesser effects depending on the settings used. The exposure variations are generally hard to detect in still images, the purpose for which the cameras and lenses were designed, however when the images are converted into an image sequence or time lapse these inconsistencies become apparent and appear as flicker.

Factor	Description (Cause/Effect)	Conclusion/Remedy
Automatic Metering modes such as Aperture/Shutter Priority and Program modes (often used when the light is expected to change such as the transitions that occur during sunset)	1/ Variations in scene brightness may cause minor exposure fluctuations. 2/ Meter's can be fooled by minor and instantaneous variations in the scene, such a bright reflection or a light moving through the scene. 3/ Camera meter's often resolve exposures in 1/3 or 1/2 stop increments which are not fine enough for a flicker free time lapse.	1/ Avoid Auto setting if possible. Use manual shutter speed and aperture settings. 2/ If unavoidable, shoot in RAW which allows exposure and colour balance to be tweaked easily and quickly.
Aperture inaccuracies	Lens are designed to allow as much light through them whilst you are focusing or composing a scene and they close down to the desired aperture during the actual exposure. At the end of the exposure they open up completely in readiness for the next exposure. The aperture may not close identically every time thereby causing flicker.	1/ Test your lenses on your bodies to see how they perform. Some lenses may have no issues at all whilst others may be problematic so know your own equipment. 2/ Use a lens wide open, but not always desirable in terms of depth of field, vignetting or sharpness. 3/ Use lenses with adapters where the lens is completely decoupled from the camera body. For example, a Leica R, Olympus or Contax (Zeiss) lens, just to name a few, adapted to a Canon body has no mechanical connection to the body so the aperture does not move at all during or between exposures so the aperture will always be exactly the same. Many older manual focus or "Alternative" lenses are ideal for this application.
Shutter inaccuracies	Most DSLR's have mechanical shutters. It's very difficult for any mechanical device to operate at 100% accuracy or consistency, 0% tolerance at all times. Shutter accuracy is less important than consistency where time lapse is concerned. Consistency can vary across the shutters operating range and might be very consistent at one end and inconsistent at the other.	1/ Test your bodies to see how they perform. Some bodies may have no issues at all whilst others may be problematic so know your own equipment. 2/ Shoot in RAW which allows exposure inconsistencies to be tweaked easily and quickly.
JPEG compression	The data collected by a cameras sensor is compressed to create a JPEG. Large degrees of compression can exaggerate minor variations in exposure.	Always shoot with as little compression as possible, ie at the highest quality setting.
Video compression	similar to JPEG compression	?
White Balance	Same as exposure variations but caused by differences in the white or colour balance in a scene.	1/ Lock down WB setting 2/ Shoot in RAW so that colour balance can be tweaked easily and quickly.

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