Skip the ND (Neutral Density) Filter and add your motion blur back in post

Neutral Denstiy Filters are a pain to use. From storing them, to attaching and removing them from the camera, to adjusting them to changing lighting conditions, they add significant hassle to video production.  For the un-initated: we use ND’s to cut down on the amount of light entering the camera so we can force the aperture wider and keep that cinematic shallow focus in our shots.

Neutral Density Filter

Neutral Density Filters reduce the light entering your camera’s lens

I’ve always been taught that ND’s were a necessity because the only alternative was to increase the shutter speed, which reduces the amount of time each frame gets exposed to light, resulting in that choppy-motion look made famous in “Saving Private Ryan”.  Unless you’re shooting an action blockbuster, this is probably not the desired look.

I recently did a filter-less shoot with my Sony RX100, which has neither built-in ND’s nor filter threads for attaching an external filter.  In post, I digitally replaced the motion blur using RE:Vision Effects’ plug-in ReelSmart Motion Blur (RSMB).

This plug-in, designed mainly for 3D graphics artists who need to add blur to their rendered objects, tracks vectors frame-to-frame and generates the appropriate blurs and streaks to mimic actual motion blur.  It can be used in two modes: RSMB (basic) and RSMBPro (advanced).  I have only used the basic mode because it has been satisfactory for my needs.

Simply drag the plug-in to your clips in your timeline and drop. That’s really about it.  If you want to tweak, there are only two parameters in basic mode:

  • Motion Blur Amount: simulates different shutter speeds.  Since cinema is universally shot with a 1/48 shutter, and this is the default setting of the plug-in, you should really just leave this alone unless going for a special look.
  • Motion Sensitivity: adjusts how much the warping reacts to motion.  I’ve found that reducing the sensitivity helps reduce warping artifacts in scenes with intense motion, but in my tests it handled almost all motion well when set at .5 or 50%.

Is it flawless? No.  If you freeze-frame some shots, you can see warping where the foreground and background mesh in weird ways. But these artifacts are hardly noticeable when played back a regular speed.

The main caveat to using this plug-in is increased render time.  So I would recommend applying it as a final step before rendering for output.  But don’t apply it to all your clips as a compound clip, or even worse as a rendered movie file, because then it will try to warp your different shots together, resulting in some very strange artifacts.

Possible scenarios where video shooters might be able to use this plug-in:

  • Run-and-gun shoots where you have to move quickly from indoor to outdoor and don’t have time/resources to add and remove ND filters
  • Shoots using cameras like the GoPro where ND filters aren’t a viable option
  • Shots going from regular motion to slow motion, which were shot at high frame rates with little motion blur in the actual footage
  • As a creative option: if you shoot your footage with little or no blur, you can effectively choose your shutter angle in post.  Maybe you want that “Saving Private Ryan” look, maybe you don’t. Now you can decide later.
  • If you’re doing post-stabilization to your footage.  Fast shutter speeds help plug-ins like Warp Stabilizer and Optical flow track the motion better; now you can replace the motion blur after stabilizing for a completely natural look.

One more note: if you really want to use an ND on your compact camera like the Sony RX100, I recommend using CarrySpeed’s MagFilter Threaded Adapter Ring with a 52mm Variable ND Filter.



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Latest Comments
  1. Lee Mackreath

    Just having a play with this in FCP X. How do you recommend adding the plugin to your project based on the issues above?..add the plugin per clip in your footage?

  2. Mark S

    Great stuff! Based on your experience, how is footage effected if you simultaneously use the RSMB plug-in with an image stabilization plug-in? Are the 2 contradictory?

    • Brandon Li

      It works great. Be sure to stabilize before adding motion blur.

      • Mark S

        What do you mean “before”? Render a movie first with stabilization, and then do a separate motion blur render?

        • Brandon Li

          In the effects chain, put stabilization first (on top), then RSMB below it.

  3. David O'Shea

    Excellent advise. Works perfectly. Next time anyone asks you how you do your handheld stuff. You could point them to this page as a starter. Stabilize then motion blur.

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