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Maintaining Relative Subject Size w/ Zoom Dolly


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#1 Liam Dale

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Posted 01 August 2010 - 12:17 PM

I wondering if anyone can tell me if there is an equation for maintaining the relative size of a primary subject during a zoom dolly (For instance: Starting 10 feet from the subject on 100mm lens - a camera dolly of 8 feet over five seconds requires an 80mm zoom to maintain the relative subject size in the frame). What is the relationship between the two movements? Thought game - would it be possible to link dolly to zoom mechanically?

-Liam
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#2 Liam Dale

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Posted 11 August 2010 - 06:05 PM

Any ideas, guys?

Maybe someone knows another visual effects board where I could ask?
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#3 Scott Fritzshall

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Posted 11 August 2010 - 09:25 PM

I don't know offhand whether that kind of equation exists, although I wouldn't be surprised if it did. Try pre-vising this out in a 3d program- set up a scene with correct proportions and a camera with the correct film back and lens settings, and play with moving the camera and zooming in.

The way you'd automate these things if you were shooting is with a motion control rig.
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#4 Liam Dale

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Posted 12 August 2010 - 12:10 AM

Thanks, Scott.

Could you recommend a capable 3d program I could track down without too much expense?

-Liam


I don't know offhand whether that kind of equation exists, although I wouldn't be surprised if it did. Try pre-vising this out in a 3d program- set up a scene with correct proportions and a camera with the correct film back and lens settings, and play with moving the camera and zooming in.

The way you'd automate these things if you were shooting is with a motion control rig.


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#5 James Steven Beverly

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Posted 12 August 2010 - 01:57 AM

Thanks, Scott.

Could you recommend a capable 3d program I could track down without too much expense?

-Liam

Blender is free, steep learning curve but there is a lot of tutorials and support and I've seen some beautiful work done with it. B)

http://www.blender.org/
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#6 Kar Wai Ng

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Posted 12 August 2010 - 10:23 AM

Thought game - would it be possible to link dolly to zoom mechanically?


The Scorpio remote focus system has an optional motion encoder module to do this exact thing. There is a kevlar belt that goes along the dolly track, the encoder reads the position of the dolly on the track, and the MDR automates zoom and focus motors to maintain the same subject size (and focus!)

And then there is full-fledged motion control...
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#7 Scott Fritzshall

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Posted 12 August 2010 - 04:25 PM

The Scorpio remote focus system has an optional motion encoder module to do this exact thing. There is a kevlar belt that goes along the dolly track, the encoder reads the position of the dolly on the track, and the MDR automates zoom and focus motors to maintain the same subject size (and focus!)

And then there is full-fledged motion control...

Oh, damn, I didn't even know that capability existed. Further evidence that I need to get on set more often...
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#8 Juha Leminen

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Posted 21 August 2010 - 07:59 PM

I wondering if anyone can tell me if there is an equation for maintaining the relative size of a primary subject during a zoom dolly (For instance: Starting 10 feet from the subject on 100mm lens - a camera dolly of 8 feet over five seconds requires an 80mm zoom to maintain the relative subject size in the frame). What is the relationship between the two movements? Thought game - would it be possible to link dolly to zoom mechanically?

-Liam



If get the dolly done and there is definition to spare, in post-production an
adjusted image scale transformation. 1920 1080 and shotted about twice the definition
it should be possible. Or would that just result in wrong effect though
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Broadcast Solutions Inc

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rebotnix Technologies

Paralinx LLC

Technodolly

FJS International, LLC

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