Motion Cadence - It's out the window so fuhgetaboutit.

With traditional filmmaking at the typical speed of 24fps, the camera operator dials in settings to create a certain amount of motion blur in each frame in order to fool the viewer's brain into thinking that all the frames are part of a seamlessly-moving sequence.  This is how we take advantage of persistent of vision, which creates temporal smoothing.  The degree of temporal smoothness is defined by the term "motion cadence."  High quality motion cadence would have no visible juddering or strobing in the image.

The typical rule for creating smooth motion cadence in a video is to double the frame rate to find the optimal shutter speed.  The is called the 180-degree rule because a shutter opened for 360 degrees is open for the entire duration of that frame.  Because we generally want to shoot at the lowest possible ISO (sensitivity) and our shutter speed is fixed (at usually 1/50th of a second), we use neutral density filters when filming to control the amount of light entering the lens.  All very simple... for 2D filmmaking when you have a typical lens.

But for 360-degree filmmaking, when using cameras with multiple fisheye lenses, there's no way to add a neutral density filter to the front of a lens, so the only technique available for controlling exposure is by altering the shutter speed or ISO.  ISO is typically set as low as it can be, and for bright scenes it's usually 100.  But even at ISO 100, on a sunny day you'd need 6-8 stops of neutral density filtration to bring the shutter speed down to 1/50th of a second. 

With a 360 camera, you'd have to bring the shutter speed up to 1/1250th or even 1/2500th of a second, completely eliminating any motion blur in the scene.  So what to do?

For outside shoots, and if you can, try to shoot in early morning, soon after sunrise... or early evening, in the hour or so before sunset.  This has two advantages... 1)  your shutter speed can be slower, providing a little more motion blur and more natural motion cadence, and 2) usually the light is more beautiful during these "golden hour" periods and your shots will be more interesting.    Think about what you're shooting and when you can shoot it and hopefully your shooting schedule is flexible.

If you can't shoot during the golden hour, and your shutter speed is ridiculously high and there's lots of movement in the frame, you can use a motion blur plugin such as Real Smart Motion Blur from RE:Vision Effects.  If there's very little object movement in frame this wouldn't be much of an issue, but when you need it, RSMB can be a lifesaver in terms of creating smooth motion.  


gblog, BlogGary Yost