Draw an accurate elipse by eye
 

Knowing how to draw an accurate elipse "by eye" can be an extremely useful tool...i.e., from rendering vases and teacups - not to mention its use in portraiture.

Here's how it is done:

Determine the outside dimensions of your elipse with a rectangle.

Connect the corners of the rectangle with straight lines (CC)

Where these lines intersect is the center, point B

Divide line BC into thirds by eye and mark with dots.

Point D is the outermost dot and will be moved verrrry slightly outward so that it is a little less than 1/3

Mark the center of the sides of the rectangle (Point A).

With a dotted curved line, the elipse will only touch the rectangle at Point A and pass through Point D.

Perspective
 

Thank heavens it works with perspective too...and that is when you REALLY need it!

In this example, I painted the elipse - my canvas and frame is really rectangular.