Falling Raindrop

Simulated Rain Drop
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Hi,
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i am looking for tips on SCALE when animating a raindrop and it’s fall from the sky.
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In general i would model the raindrop, put the camera on top of it (maybe throw in a little constraint so that the camera can move around as it falls).
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My problem is scaling of the environment: any tips? It should fall from lets say a “felt” kilometer, and sizing in Blender has always had a question mark attached to my thoughts…
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thx for Your help!
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Dennis