Free Camera setup - The Hitchcock Zoom (AKA the Vertigo Effect)


I've just been having a play around for my own satisfaction, and attached is a Lightwave scene containing a Camera parented to a null. As the camera raises or lowers on it’s Y axis, or dollys in or out on it’s Z axis, an expression drives the camera’s zoom factor ensuring that the vertical field of view always passes through the null. Just make sure your object which you want to be the focus of the shot is above the null, and move the camera in or out, and you will get the perfect 'vertigo' effect.

The expressions used are:
VFOV - This determines the Vertical Field of View, in degrees. It is essentially trigonometry to calculate the field of View based on the distance and height to the null. This isn't linked to anything, but it is referenced by the other expression.

2* (asin([Camera.Position.Y]/vmag(Camera.wpos(Time)-CAMERA_REFERENCE.wpos(Time))))

ZOOMFACTOR - This expression changes the Field of View into the Zoom Factor.

((0.7362*25.4)/ tan(([VFOV])/2)/2)/9.35

The 0.7362 is the Frame width of a 35mm frame. If you change the frame size, this will need to be adjusted accordingly. If the Frame Width changes, so does the conversion between Focal length and Zoom factor.
The 9.35 we divide by at the end is what the Focal length of a camera with a 35mm Frame size is when the Zoom factor is set to 1.0. (Because the figure displayed in the camera properties panel is limited to a single decimal point, it will round to 9.4. If you set the Zoom factor to 10, and then divide the given Focal Length by 10, you get the correct figure.)

So if you want to change your camera's Frame Width, set the Zoom Factor to 10, and replace the 9.35 at the end of the expression with a tenth of whatever is displayed as Focal Length. Then replace the 0.7362 in the expression with whatever value your new Frame Width has.

Hopefully somebody will find this of use, or interest.




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