Here is a scribble for some camera trigonometry. couldn't attach it to a post in the forum so I'll just park it here and link to it.
Keep in mind that if you have an image / image sequence that corresponds to the camera (i.e. match move), then the horizontal aperture and vertical aperture need to reflect the image aspect, otherwise your render won't match the scans.
And from the good ol' Shake docs:
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