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tjer

Lens used in shot

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Hi All,

 

I am working on a shot where I need to composite on some 3d geometry. Also I want to know what type of lens they used... I remember that there was a tutorial about how to calculate this! If anybody can help me with this it would be great!!

 

Cheers,

 

Thierry

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I'm not sure what example you are referring to. However, if you don't know the lens properties of the camera you could use a high end tracking software such as PFTrack (or use any other tracking software that allows you to input lens parameters) and just guess + check a ground plane with the footage until you nail it. PFTrack, Boujou and other softwares let you add dummy objects to test the tracking as well. If the footage was shot and unedited from a high end cam you could possibly be able to see the lens properties in Abode Bridge if you look at the meta data of the file.

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There is no way to calculate a lens 100% just from existing footage. Even matchmoving apps kinda guess it based on their analysis or require the user to help along by visually matching the distortion patterns using some graphical overlays. Still, it is just one possible solution out of several ones that are mathematically solvable. The bitch of it being, that all angular math is ambiguous without a single fixed variable in the equation. So unless you can provide a reference measure e.g. a known dimension in the image, the lens filmback size, focal length, a known angle etc. as that fixed variable, the calculated solution and lens may work logically, but must by no means represent any of the realworld conditions. Ultimately this still means, you must kinda know which lens they used to begin with...

 

Mylenium

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Not sure, but I think ARRI cams retain that info in ther operation logs in some form and I also believe there is some of that in the specs for XDCAM and P2 formats, but obviously it would depend on the cam operator and camera model having set the options to actually write that data, which often isn't the case...

 

Mylenium

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Most of the newer DSLR cameras store lens data. A few motion cameras store it in metadata if you are using compatible lenses. I know RED and the new Cooke's do it. I would assume the RED lenses do, but I don't remember.

 

We mostly us PFTrack here and yes, you can usually get pretty close if you have a good reference frame (meaning you can find a frame that has a good selection of horizontal and vertical lines) to use as reference. But it's always a little hit or miss. I'm pretty sure there is a tutorial on the PFtrack site.

 

On a professional shoot you would usually get lens notes from the AC as well as a reference plate for every VFX shot, which consists of a checkerboard pattern held at a 45-degree angle to camera.

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