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How to calculate correct size of green screen


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#1 There Yougo

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Posted 17 September 2015 - 01:48 PM

Hi!

I'm about to start to shoot a production in a studio, where we will have a broad object of about 5m(16ft) length and 2m(6ft) height.

Now I am trying to figure out, how wide the greenscreen in the back needs to be.

 

I think it might go like this:

It all depends on 3 things:

- My focal length

- Distance between camera and object

- Distance between object and green screen

 

 

My focal length will be 50mm. On a super35 sensor, that gives me a FOV of about 24 degrees.

 

First question now is:

If I need the object to be frame filling from left to right, how far does the camera have to be positioned from the object (with a 50mm lens)?

 

Second question:

If the distance between the object and the green screen is about 4m (that should be a good distance to avoid spill, right?), how wide does the green screen need to be, when I'm on a 50mm lens?

 

 

Thanks a lot!  :)


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#2 dan kessler

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Posted 17 September 2015 - 03:49 PM

All you need to know is the distance from the camera to the green screen.  Just calculate based on your field of view.

However, you don't necessarily have to fill the whole frame with green. If you just want to extract a matte for your foreground subject, the screen only needs to be big enough to put a green border around that subject.  Everything else can be garbarge-matted out.


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#3 David Mullen ASC

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Posted 17 September 2015 - 04:36 PM

http://www.pointsinf...=50&dst=32&u=us

 

According to this calculator, at 10m on a 50mm lens in Super-35, the horizontal view would be 5m, the width of your object.  So adding 4m to that, your green screen would be 14m away, so you'd need a 7m wide screen.  But I would think you'd want to see a little off each end of the object, so you might want to push it back a little towards the screen, or back up the camera a little and expand the size of the screen.


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