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Slow down a null exponentially
I having a panning shot of a building from the sky down to the ground.
I need to do a sky replacment.
I can track a feature position on the front of the building and attach a null.
Now I want the sky in the back to move with the pan but obviously a lot slower, exponentially than the null.
What expression can I use to exponentially slow down the position of the null data when parenting the sky to it? Something on a sliding scale as it were.
I’d prefer not to have to do a camera track given the brevity of the scene and am happy with “eyeballing” the speed of the sky.
Ref:
Thanks for your time!
Chris
Orchard Film Studios, Canada
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3 Replies
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I think you’ll have to define a reference starting y position for the null and then use something like this:
startY = 150;
mult = .5;
deltaY = thisComp.layer(“tracked null”).transform.position[1]-startY;
value + [0,deltaY*mult]If the null is keyframed, you might define the reference y this way:
startY = thisComp.layer(“tracked null”).transform.position.valueAtTime(0)[1];
Adjust the value of mult to get the tracking you want for the background.
Dan
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Thanks Dan, as always you save the day – and in record time!
I also had a slight left shift so modified to affect the x, I know there would be a cleaner way but did this:
startY = thisComp.layer(“Null 1”).transform.position.valueAtTime(0)[1];
startX = thisComp.layer(“Null 1”).transform.position.valueAtTime(0)[0];
mult = .7;
deltaY = thisComp.layer(“Null 1”).transform.position[1]-startY;
deltaX = thisComp.layer(“Null 1”).transform.position[0]-startX;
value + [deltaX*mult,deltaY*mult]Works like a charm!
This is for a submission to Sundance, and I know it won’t be your first, but thanks for contributing – your work indirectly appears in many great features I’m sure!
Kudos!
Chris
Orchard Film Studios, Canada
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Let me point out, from a “physics” pov, that there would be no parallax effect on the sky during a panning shot. Just to be technically clear.
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