Motion Blur

Rodrigo Iturralde · March 18, 2009

Hi I want to make slow speed motion blurred images on film. I have done some research and I have ended with a solution but I am not sure this will work as it does with video. I have not done any tests, but I do know film cameras allow to close shutter but I want to open it more than 180 degree how can I do this ? Can someone help?

I plan to use an Arri 2C to film at 6 frames per second and then make a telecine at 6 frames, any suggestions. I have not done tests but I am planning to do them, I want motion blurs as in still photograhy can be achieved with a shutter speed of 1/15 more specifically but trying to keep the perception of time as normal as possible.

Answers are more than welcome, Thanks

John Sprung · March 18, 2009

With the Arri 2C, your maximum shutter opening is 180 degrees, no way out of that. The problem is that it takes time to physically move the film from one frame to the next. There are some very rare and unusual cameras that can give you a significantly bigger shutter angle, but none practical for your project. I have somewhere an old Acme Kinescope movement that was used with a 288 degree shutter, but that was just for recording NTSC TV in the early 1950's, before video tape.

-- J.S.

Chris Millar · March 18, 2009

Doesn't the 2C have a sort of 1:1 shaft access for inching ?

If so you could make an intermittent inching system...

Spin 180 as fast as it'll go

Stop for shutter shut

Spin 180 as fast as it'll go

Stop for shutter open

All within your 6th of a second

Spin 360 as fast as it can

STOP for desired exposure

...for maximum shutter angle possible

to be stopping and starting at 6fps (12 times actually) it'd have to be a motor of reasonsble torque and good design - the electronics would be a chore depending on how much user interface you want

Scott Fritzshall · March 18, 2009

You need to calculate how much motion blur you want in order to know how long to keep the shutter open for. But keeping the shutter open on a motion picture camera (beyond 180deg on most film cameras, and 360deg on video cameras) inherently involves reducing the frame rate, and reducing the frame rate will ruin the sense of normal motion. You could maybe get away with 18fps and still have it look relatively normal, but anything beyond that is pushing it. If you want normal motion but extreme motion blur, you're going to need visual effects trickery.

If you shoot at a higher frame rate and then run it through some optical flow processing such as Kronos, you should be able to both retime it so that it runs at normal speed, and use the derived motion vectors to add extra motion blur. I actually just tested this on a shot that was filmed at 120fps- I retimed it to 24fps but set the "shutter" to be longer than normal. It works fairly well, but you'll probably need to put in some time to draw mattes for the different layers and parts of the things that are moving, because optical flow tends to get stuff wrong without your input, which leads to wierd smeary artifacts.

Rodrigo Iturralde · March 19, 2009

With the Arri 2C, your maximum shutter opening is 180 degrees, no way out of that. The problem is that it takes time to physically move the film from one frame to the next. There are some very rare and unusual cameras that can give you a significantly bigger shutter angle, but none practical for your project. I have somewhere an old Acme Kinescope movement that was used with a 288 degree shutter, but that was just for recording NTSC TV in the early 1950's, before video tape.

Thanks, I´ll try to look some into the old cameras.

-- J.S.

Rodrigo Iturralde · March 19, 2009

Doesn't the 2C have a sort of 1:1 shaft access for inching ?

If so you could make an intermittent inching system...

Spin 180 as fast as it'll go

Stop for shutter shut

Spin 180 as fast as it'll go

Stop for shutter open

All within your 6th of a second

Spin 360 as fast as it can

STOP for desired exposure

...for maximum shutter angle possible

to be stopping and starting at 6fps (12 times actually) it'd have to be a motor of reasonsble torque and good design - the electronics would be a chore depending on how much user interface you want

Thats a good one, I actually have thought of this before, arri 2c has a shaft which can be operated manually but it will be kind of a challenge to trying to make it work at 1/15 of a second. But I have talked with a friend who is an arri ceritified technician and some kind of inventor, he usually repairs cameras and makes modifications on them and he told he´ll think a way out to modify the camera or make up some system to work for this.

Rodrigo Iturralde · March 19, 2009

You need to calculate how much motion blur you want in order to know how long to keep the shutter open for. But keeping the shutter open on a motion picture camera (beyond 180deg on most film cameras, and 360deg on video cameras) inherently involves reducing the frame rate, and reducing the frame rate will ruin the sense of normal motion. You could maybe get away with 18fps and still have it look relatively normal, but anything beyond that is pushing it. If you want normal motion but extreme motion blur, you're going to need visual effects trickery.

If you shoot at a higher frame rate and then run it through some optical flow processing such as Kronos, you should be able to both retime it so that it runs at normal speed, and use the derived motion vectors to add extra motion blur. I actually just tested this on a shot that was filmed at 120fps- I retimed it to 24fps but set the "shutter" to be longer than normal. It works fairly well, but you'll probably need to put in some time to draw mattes for the different layers and parts of the things that are moving, because optical flow tends to get stuff wrong without your input, which leads to wierd smeary artifacts.

thanks for the info, I think I can sacrifice a little bit of the normal sense of motion and have something more like an animation and have this sense of normal sensation maybe by joining each frame with dissolves, but I find more important the amount of blur. Today I was at location and shot 24 frames in one second with a Canon Eos 5D Mark II camera at 1/4 of a second, the results were awesome. I am planning to back-up my experiment by shooting like this. But still looking a way out for doing it on film. I will post my experiment results for all of you to see how everything is turning out.

Rodrigo Iturralde · March 19, 2009

thanks for the info, I think I can sacrifice a little bit of the normal sense of motion and have something more like an animation and have this sense of normal sensation maybe by joining each frame with dissolves, but I find more important the amount of blur. Today I was at location and shot 24 frames in one second with a Canon Eos 5D Mark II camera at 1/4 of a second, the results were awesome. I am planning to back-up my experiment by shooting like this. But still looking a way out for doing it on film. I will post my experiment results for all of you to see how everything is turning out.

here it is the effect desired done with a digital camera, in the actual shot one person will be static in the middle with no blur at all.

Edited March 19, 2009 by Rodrigo Iturralde

Rodrigo Iturralde · March 19, 2009

here it is the effect desired done with a digital camera, in the actual shot one person will be static in the middle with no blur at all.

This is more like it

Scott Fritzshall · March 19, 2009

How did you shoot 24fps with a 1/4 second shutter? That doesn't make sense- the longest shutter you could possibly get at that frame rate is 1/24th of a second. To get exposures of 1/4th of a second, you'll either need to shoot at 2fps with a 180deg shutter on a film camera, or 4fps with no shutter on a digital camera, or you'll need to do that in post.

Chris Millar · March 19, 2009

How did you shoot 24fps with a 1/4 second shutter?

beam splitter, many cameras crystal locked but out of phase with each other - post sorting of frames - non digital if you have the time ;)

Will Earl · March 19, 2009

How did you shoot 24fps with a 1/4 second shutter?

I would imagine (and I am only guessing) is that with an electronic sensor you be able to stack up the previous frames - in the case of 1/4@24 you'd need to add the previous 11 frames to the current frame (if my maths is correct) to get an slow shutter effect.

You could possibly (I haven't tried it, I'm rubbish with colorX expressions) do a similar thing in post with film by adding previous frames to the current frame (something like: colour = colour@time + colour@time-1 + colour@time-2 + etc). You would need to compensate for the increased exposure (colour = colour / 12).

Rodrigo Iturralde · March 19, 2009

How did you shoot 24fps with a 1/4 second shutter? That doesn't make sense- the longest shutter you could possibly get at that frame rate is 1/24th of a second. To get exposures of 1/4th of a second, you'll either need to shoot at 2fps with a 180deg shutter on a film camera, or 4fps with no shutter on a digital camera, or you'll need to do that in post.

Sorry I meant 24 shots at 1/4 second shutter, that I will regroup at the editing as 24 frames per second. But actually I am planning to do it on film at a 3 frames per second. I could use video or do it in post but actually I need it directly on film for one particular reason, postproduction costs and time.

Thanks again