# How to model an accurate parabolic mirror with a known focal point?

I am new to Blender and really enjoying it now, but... I want to make an accurate parabolic mirror with a known focal point. For example, I would want to have it focussed so that a parallel beam could be reflected from the focal point outwards.

This will be 3d printed and then used with a tiny sonic transmitter/receiver set up to map surroundings, for a small rover bot. I think this could be done with a Bezier Curve, at least the general shape could be emulated. But how to make the parabular accurate for the focal point? I am guessing that once the general shape was made, it could be extruded away from the front to make it more solid.

The focal point needs to known so I can add struts to mount the sonic electronics. I'm not worried about scale or size at this point, just the method that I can repeat. Ive looked for some scripts that might help, but not found anything yet.

Enable the add mesh extra objects addon, then from add menu choose add > mesh > math function > math z surface
(x ** 2 + y ** 2) / (4 * f)