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problems with motion blur / objekt speed


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#1 Robert Patzelt

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Posted 12 November 2010 - 06:39 AM

Hi evryone.
I `m looking for help with the folowing problem. We are shooting a 35mm movie and have done some VFX shoots. We shoot a scene with a streetcar , where an actor is hanging outside. Regarding the budget the VFX supervisior where asking for not panning the camera. we have done 3 different sizes and angels with two cameras at the same time. All the shoots get a reasonible motion blur / shuttering. I thing it s a " simple " shutter effect because the streetcar went`s in less then 3 1/2 seconds through the frame. The other thing is that the " actor" looks like a " double Image". on every frame.( it was a night exterior shoot with lit greenscreen in the windows behind the actor) ?.
We have to re shoot the sequence , and i have propose to extend the time how long the streetcar is in frame. Did any one have any charts of how long the object must be in frame that it is " shutter free". I get charts for " recommended panning speeds" but no information for fix camera position. Or did some one knows a formula so that i can calculate proper speeds for different lenses and distances !?. Would a change to a 90 dgree shutter angle minimate or solve the problem !?.
Thanks a lot for any answer in advance , and please excuse my poor english.
Robert

Edited by Robert Patzelt, 12 November 2010 - 06:40 AM.

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#2 Thomas James

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Posted 13 November 2010 - 03:18 PM

Digital 2K cinema now supports the projection of up to 48 frames per second. Cinematographers such as James Cameron have promised to shoot and project the fast action sequences of their next movies at 48 frames per second.
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#3 Chris Millar

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Posted 13 November 2010 - 11:55 PM

Firstly, shut up Thomas.

Secondly, er... Too many variables left open with a vague description of a problem - hard to diagnose, let alone understand - can you post the footage ?

(maybe someone else knows what he means??)
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#4 Robert Patzelt

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Posted 15 November 2010 - 03:36 AM

First thanks for answering. To make it simple : did someone get some charts about how long a filming object has to be in frame with witch lense without getting it " shuttered" . Or is the " old " 7 second rule fine !?
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#5 Chris Millar

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Posted 15 November 2010 - 04:54 AM

Anyone know what he's talking about ?

The 7 second rule sounds interesting ...

:huh:
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#6 Robert Patzelt

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Posted 15 November 2010 - 09:03 AM

Anyone know what he's talking about ?

The 7 second rule sounds interesting ...

:huh:

Hi Chris. The seven second rule i have bben teached by an polish DOP when i was focus puller. It says " everything what comes in frame on left ( or right ) side and will not exit on the right side of frame ( left side ) before 7 seconds will be for shure not shutterd. If it`s faster then you have to pan with the object to keep it for 7 seconds in frame.
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#7 Chris Millar

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Posted 15 November 2010 - 01:41 PM

What do you mean by 'shuttered' ?

Motion blur ?

Remember that in physical film projection each frame is projected twice (48Hz), but the same footage viewed digitally 24p (24fps) wont be ...

Maybe do you mean the artefact of 48Hz projection (24 frames each shuttered twice) ?
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#8 Thomas James

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Posted 15 November 2010 - 08:56 PM

Robert, the reason why you see a double image is because of eye tracking artifacts. The human visual systems anticipates motion along a motion vector. However if the motion that is projected lags behind this confuses the human visual system and causes a double image to appear.
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#9 Robert Patzelt

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Posted 16 November 2010 - 03:43 AM

What do you mean by 'shuttered' ?

Motion blur ?

Remember that in physical film projection each frame is projected twice (48Hz), but the same footage viewed digitally 24p (24fps) wont be ...

Maybe do you mean the artefact of 48Hz projection (24 frames each shuttered twice) ?


" shuttered" for me means : an effect that is similar to strobe effect , it`s happend normally when you pan to fast .
Robert
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#10 Sean Lambrecht

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Posted 16 November 2010 - 06:09 AM

I think "shuttered" is being confused with "stuttered"... Whereas as object moving across the screen will not appear stuttered if it take 7 seconds or longer to pass from one edge to the other. The ASC manual has charts on panning speeds in relation to focal length and frame rate. I would guess that some VFX shots could require a higher shutter speed to get very clean, sharp edges, and the effect of shutter blur would be added later.
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#11 Chris Millar

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Posted 16 November 2010 - 01:53 PM

Anyhoo,

Unless you're trying to match the motion blur from plate to plate and that is ineed the problem you're trying to explain (?) then it wont affect the VFX - it's only a visual artefact (Thomas explained it pretty well!) - the VFX program/process doesn't 'see' the way we do.

In fact having the usual visual artefacts on your VFX work might assist in creating the illusion of reality.

But if it the matching of motion blur from one plate to another then shutter angles will be your friend.

Yeh ?
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