Scaling centred on one of the foci of an ellipse

How to I set the origin of scaling so a an ellipse scales around one or the other of its foci rather than the geometrical centre?

Position the 3d curser where you want to the scaling to centre and set the 3d curser to be the pivot point (drop down list on the 3d view header or period key on the keyboard)

I’ve just tried that - I moved the 3D cursor to one of the ellipses foci and set it as the pivot point. However, it does not scale about the focus point of the ellipse. The geometric centre of the ellipse does not move, but it should if its scaling about one of its foci

This was not the solution. Is there a way to scale an ellipse about one of its foci?

Show us exactly what you want to happen (screenshots and blend file)

Okay, this is how I wanted the scaling to work. With a ellipses focus at [0,0,0] I’ve shown initial and final ellipses and some intermediate sizes scaling it just in the x-axis to keep it simple. I hand calculated the position for each ellipse.

For reference the hand calculation I used is: y-location = sqrt(Y^2 - X^2) where Y and X are the y-axis and x-axis radii. Y is fixed at 5 units. X varies - 2.5, 3.0, 4.5, 4.9, 5.0

EDIT: now correctly attached the blend file and removed the failed attempts


orbi.blend (537 KB)