Parabola for 18 aluminum mirror

[jixon]

Parabola for 18" aluminum mirror

Help; need to configure inputs into parabola formula to machine an 18" dia., 1.5"h aluminum disc. for use as primary objective mirror in telescope.

 

[Chronos]

Depends on the focal length. At f10 it little matters. What focal length do you have in mind?

 

[jixon]

Focal length 79.2", 0.256 in. @ apex; f/4.4

Using a CNC lathe but need inputs for autocad program to 'run' lathe for accurate cutting. Removing 32.53 cu. in. material.

Not sure what to plot for points along 'x' to perimeter from center, depth of 'y'