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RED 4k downscaled to 1080p and C4D camera matching
Here’s the production plan:
We’re going to shoot green screen at 4k 16×9 (4,096×2,304)on the RED One. Using RED CineX we’ll downscale down to 1920x1080p QuickTime files.
Using P-Cam I’m able to calculate the focal length match between the RED and a theoretical 2/3″ HD camera shooting 16×9. For example, a 50mm lens on RED at 4k 16×9 should be equivalent to a 21.7mm lens on the HD camera. So far so good.
Now in C4D I need to set up the 3D camera. I have two essential parameters to match. FOCAL LENGTH and APERTURE WIDTH.
Here’s the question: if I assume square pixels on the virtual sensor (back plane) and assign to APERTURE WIDTH a real world measurement (such as a from a Sony F900) will field of view match?
Am I going about this the right way? Am I better off calculating the field of view based on the Focal Length and subject distance and working backwards from that?
– JC
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3 Replies
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I’m not sure what the answer is, but if you’re actually going to track the footage in Syntheyes, Boujou, or equivalent, then the imported file should include a Cinema camera with the appropriate settings.
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Good idea. However, there’s more.
The issue is that we’re using C4D to previz the whole project and set up our camera including lens choices based on that so that all the 3D will look just right in post (field of view, perspective, tilt, camera height, etc.) In this case, deriving the data after the fact – while it would work – won’t satisfy the creative intent.
I may have figured out a solution. Some research reveals that the horizontal width of the F900 sensor is 9.58mm. Adding that info into C4D lines up with what pCam tells me within 2/10ths of a degree for Field of View.
I’m still curious as to the best approach. Someone has surely worked this out in the past. It should be a simple matter of working out the math.
– JC
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I think it’s just a matter of plugging in the aperture width of the sensor and the actual (not interpolated) focal length of the lens.
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