A Little Slow Motion Q&A
Viewer, Jonathan Scruggs, left a comment on Izzy Video 39. My thinking is that several people might be wondering the same thing, so I’m posting the question and answer here.
Jonathan writes:
I realize this is a little off topic but i had a question about slow motion. when you shoot at high frame rates the picture at normal speed looks jittery and strobe-like, and when you slow down video shot at normal frame rates the picture doesn’t look very smooth. logically, a newbie like me would think that if you shoot at a higher frame rate you would get smoother more cinematic slow motion. am i on the right track?
By the way, Jonathan clarifies in a follow up comment that he intended to say “shutter speed” instead of “frame rate.”
Well, the answer to your question is…it depends.
Slow motion with video is complicated for several reasons:
With video, we have no control over the frame rate, so the normal method of shooting more frames (like we would do with a film movie camera, for instance) is not an option. We can’t shoot real slow motion, so we have to fake it.
What do I mean by fake it? We shoot at a normal frame rate of roughly 30 frames per second, and then let our computer create the additional frames to put between the original ones. It does this by blending the images on the original frames.
Now here’s where the problem comes in. Because normal video is interlaced, when we slow it down or create a freeze frame, and view it on a television, we frequently end up with a “flicker†because televisions display the video in interlaced format.
Strobing can also happen when you use a fast shutter speed because the original images are less blurred to begin with. Sometimes we want more motion blur.
I recommend the following three steps to improve slow motion video results:
- Shoot in progressive mode. This is the opposite of interlaced video. If your camera doesn’t have progressive (also sometimes called “Frame Mode†such as on my Canon GL2), then shoot regular interlaced video and apply a “de-interlace†video filter later in your editing software. This will have a similar effect.
- Shoot at a normal shutter speed (1/60 of a second). I’ve personally had the best results by doing this, but it does depend on the how I’m going to use the slow motion. If I need to see my child’s fingers perfectly in a football game, for example, then I should probably speed up with shutter speed so there is less “motion blur.â€
Usually though, I like motion blur in the original frames, because later when the computer generates the filler frames to go between the original ones, the new frames will be blended images of the original blurred images. The overall effect appears smoother and less “strobe-likeâ€. In my opinion, having a good amount of natural motion blur in the original footage helps produce smoother slow motion later.
- Apply a de-flicker or de-strobe filter to the video within your editing software, so when you play the video on your television, you won’t have that annoying flickering effect in the freeze frames or slow motion parts.
Using all of these techniques in combination should yield improved slow motion video. However, keep in mind that with a fixed frame rate, slow motion will never look as good as film.
Think Gatorade commercial, and you’ll know what I’m talking about here.
