Reducing Flicker

7/28/2019 Reducing Flicker

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reducing flicker for stop-motion animation and time-lapse photography

If you’ve ever tried your hand at stop-motion animation or time-lapse photography, chances areyou’ve run into the common problem of inconsistent lighting or luminance variation betweenconsecutive pictures taken on the same camera, with the same lens and settings. This issue is

usually referred to as flicker. There are many causes of flicker, including–but not limited to–auto camera settings, the type of lensused, high aperture settings, fast shutter speeds, Av stepping, Tv stepping, natural lighting changes,incandescent and fluorescent lighting, fluctuating electricity, clothing worn while animating, and thematerials that are being photographed.

This article provides solutions for reducing flicker, both during shooting and in After Effects.

camera settingsMake sure that all auto settings on the camera body and lens are turned off and set to manual. Any

auto settings, such as auto-exposure, auto white balance, and light optimizer will usually causeluminance variations from shot to shot.

Use a slower shutter speed. Fast shutter speeds are also a common cause of flicker. For example,DSLRs cannot really be consistent from frame to frame when shooting at extremely fast shutterspeeds. Instead, use an ND filter to compensate and keep the exposures to 1/30th of a second orgreater.

For time-lapse photography, use a constant Av value and a bulb exposure if possible. This will help toprevent Av-stepping or Tv-stepping, which is a 1/3-stop jump in the iris or shutter speed that oftenhappens while shooting from sunrise to sunset during an Auto Ramp time-lapse. Since bulb exposuretimes can be set with a precision of 1/1000 of a second, it’s possible to produce more gradualchanges and reduce flicker.

Using auto-focus will not cause flicker, but it will most likely cause differences in the focal planedepending on the depth of field and movement within the shot, resulting in a different and potentiallymore severe problem. For stop-motion animation, it’s especially important to control the focusmanually.

the lens

More often than not, the camera lens is what causes stop-motion flicker. Most modern lensescommunicate with the camera body to assist the photographer in setting focus and exposure. Stop-motion flicker, often found in animation and time-lapse photography, usually occurs because the lensis wide open until the shutter or depth-of-field preview button is pressed. At this point, the lens stopsdown to take a picture or preview the depth of field. However, most modern digital cameras controlthe aperture of the lens from the camera body. And, since the camera controls the aperturemechanically, friction causes minute differences in the exact size of the aperture as the iris bladesclose each time a photograph is taken. Therefore, there’s a possibility for minor variations inluminance from shot to shot.

It’s very important to know each of your lenses. For instance, a Canon 16-35 II probably shouldn’t bestopped down past f/5.6. At f/16, most 16-35s will flicker. But, a Canon 50mm f/1.2 might start to





lighting

Make sure that all of the bulbs in your lights are functioning properly. Bulbs often pop when the lightsare turned on, so it’s a good idea to test all of them before shooting each day and watch for anydimming issues. This is an especially good idea if you plan on using more lights for another setuplater on in the day. Hot light bulbs used in Mole Richardson lights tend to dim before they’re about toblow. Sometimes, the bulbs themselves darken, so you can visually see if they need replacing.

LED light panels are also great for both stop-motion and time-lapse photography. It’s true that LEDsflicker, but the rate at which they flicker is usually imperceptible to the human eye. Non-rectifiedLEDs, such as cheap Christmas lights, flicker at 60Hz, which is more likely to be noticeable, whereasrectified LEDs flicker at 120Hz, which should be virtually unnoticeable. The upside to using rectifiedLEDs is that they’re 30-40% brighter than non-rectified LEDs. The downside is that they’re lessefficient. However, LEDs are still more efficient than most other light sources on the market.

If you’re using cheap fluorescents other than Kino Flos, or other non-flicker fluorescents, it’s a goodidea to shoot at a very long exposure. Fluorescents constantly flicker, but usually a 1-2 secondexposure should keep the images balanced.

Last, if you’re shooting in a studio, make sure that no light from outside–no matter how small–ispolluting your shooting space. Also, make sure that all gels, screens, or other objects in front of thelights are tied down properly and not moving around due to airflow issues, such as a ceiling fan or abouncing c-stand arm.

clothing

Wear dark clothing. Most stop-motion animators wear entirely black outfits while shooting to reducethe risk of light reflecting off their clothes. This may sound silly, but it’s actually a very commoncause of stop-motion flicker. Also, black duvetyne is a highly opaque fabric commonly used in filmstudios for blocking and absorbing light.

sets, objects, and puppets

Know the limitations of the sets, objects, and puppets you’re shooting. Porous materials such aswood and foam are affected by moisture, and therefore they may expand or shrink depending on theweather and the time of day. This won’t necessarily cause flicker, but it can cause unwantedmovement, which might be mistaken for flicker at first glance.

Also, watch out for highly specular materials that might be lying around or hanging on the walls of the shooting space. Mirrors, metallic objects, or pieces of Mylar left by a previous animator may bethe ultimate cause of unwanted flicker.

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Reducing Flicker