How can I work out how far away I need to be from the set to get it all in frame?

Question

I am planning on shooting a bedroom from above. I am planning on getting a high ceiling studio if I can, and I want the bedroom I build to be the same aspect ratio as the camera lens (so, 16:9?). But I need to work out how far away I need to be, with a 24mm lens (to avoid any warping?) on a 5d or c300 perhaps, to get it all in shot. And what my limitations are on the size of the room. Any thoughts on how to work this distance out without access to the studio or set yet?

Answer 1

The math behind this isn't really complicated. The basic version is that the angle of view depends on the sensor size and the focal length of the lens. You can work it out*, but there are a lot of handy calculators online. The TawbaWare web site has a number of handy ones, including a couple for field of view. The dimensional FoV calculator will probably be the most helpful to you — put in your 24mm lens, 1 for the "focal length multiplier" (since you intend to use a full frame camera) and then experiment with different subject distances until you get the size you want.

As an aside: camera lenses project a circle, so they don't really have an aspect ratio — it's the sensor that has one. For most DSLRs, the native aspect ratio is 3:2, but if your final goal is a 16:9 image you can of course just worry about the long edge and then crop.

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_{* If you're curious: double the arctangent of half the sensor width times the focal length}