Water streak effect

[George Ebersole]

For mosters and time lapse shots there's an effect where falling water or water rushing over rocks gets all fuzzy, blurry and in general cool looking.

 

Has anyone tried to achieve this with digital video?

 

If so, how did you do it?

[Max Field]

Link a sample of it?

[David Mullen ASC]

To get moving water like in a river to be streaked requires very long per-frame exposures, which isn't possible when the camera is running at 24 fps where even with a 360 degree shutter angle (no shutter at all) the max exposure time is therefore 1/24th of a second. You'd have to shoot at a very low frame rate (like 2 fps, etc.) and then stretch it make to normal speed in post, but then the motion of people in the shot will also be blurred and very steppy due to the low sampling rate.

[George Ebersole]

Yeah, I thought it might require some post work, but I thought maybe someone had figured out a cheat or a workaround to get the same thing in camera.

[David Mullen ASC]

Heavy motion blur requires longer-than-normal exposure times. Once you go to a 360 degree shutter angle, the only way to increase per-frame exposure time is to drop the frame rate.

 

The Canon XL1 DV camera had such a feature for low-light photography where they reduced the frame rate, got longer exposures, and internally restored the motion speed back to normal.

[George Ebersole]

And yet another reason I'm kicking myself for not buying a Canon.

[Sarah Thompson]

I haven't tried this, but I am pretty sure it would work:

 

1. Lock the camera down really solidly so there is no movement at all in terms of pan/tilt.

2. Shoot the scene at as close as possible to a 360 degree shutter angle.

3. Frame rate can be anything you like depending on the kind of movement you want.

4. In post (ideally in After Effects or Nuke, but I'll explain for After Effects), import the footage into a new comp. Create a black solid and put it below the footage. Set the footage layer to a low level of opacity and choose an additive blend mode. Then make a large number of copies of that layer and offset each of them in time by 1 frame. You'll need a LOT of them, enough to span 10 to 30 seconds depending on your frame rate.

 

This will effectively give you a 10 to 30 second exposure for the water, but with a rolling window so you still get movement.

 

If you have elements you don't want to blur, add another layer at the top of the stack set to normal blend mode and be prepared for some work because you will need to roto masks for them. Another option would be to shoot the live action separately from the water -- I'd keep the camera locked down between both shots, but for the live action I would go back to a 180 degree (or whatever your preference) shutter so the movement doesn't look weird and set up a portable popup green screen behind the actor(s). This would give better looking movement whilst letting you pull a key so most of the roto can be avoided.

[Phil Rhodes]

I think you can probably make it do that with the time remapping, if you set the comp shutter angle to some suitably large value.