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Correct answer Rick Gerard

The stroboscopic effect happens when the frame rate and motion in the frame collide. The phenomenon is often called Judder. It is why the wheels on a stagecoach sometimes appear to be turning backward or why rolling credits seem to studder. Generally, if things move an even number of pixels per frame, the movement is smooth. There are certain speeds where the movement is reversed or even frozen. If you have a bunch of horizontal lines that are exactly 10 pixels apart and the layer is moving vertically at 10 pixels per frame, there will be no movement visible in the frame because each successive line will be in the same position as the preceding line was in the previous frame. 

 

I hope this helps. 

2 replies

R
Community Expert
Rick GerardCommunity ExpertCorrect answer
Community Expert
May 24, 2022

The stroboscopic effect happens when the frame rate and motion in the frame collide. The phenomenon is often called Judder. It is why the wheels on a stagecoach sometimes appear to be turning backward or why rolling credits seem to studder. Generally, if things move an even number of pixels per frame, the movement is smooth. There are certain speeds where the movement is reversed or even frozen. If you have a bunch of horizontal lines that are exactly 10 pixels apart and the layer is moving vertically at 10 pixels per frame, there will be no movement visible in the frame because each successive line will be in the same position as the preceding line was in the previous frame. 

 

I hope this helps. 

Mylenium
Mylenium
Legend
May 24, 2022

It's just motion stutter, which happens when the temporal samples/ "time slices" of the composition frames unfavorably coincide with the timing of your animation. Most often this is asked in relation to judder on scrolling credits and titles, so if you look that up, you can find plenty of explanations on why it occurs and how to combat it like tweaking the timing to avoid "crooked" keyframes, using motions blur, tweaking shutter duration and phase on the 3D camera and so on. In your case also using a camera with a longer focal length might help, as from your clip it seems you're using a very short one which causes a lot of this extra uncontrolled parallax movement that makes the problem stand out even more.

 

Mylenium

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