I was trying to explain the method I use for drawing ellipses to a friend today, and it sounded so much more complicated than it is to draw. So, I'm attaching a couple of my preliminary sketches from today's painting.
Initially, I sketch the ellipse in as a rectangle, and then, I divide it both vertically and horizontally. Once you have it segmented, it is easy to draw the ellipse within the rectangle. The bottom portion should be the exact reverse of the top portion. And the left should be the reverse of the right.
With your OMS, you can remove the initial rectangle and refine the ellipse as you paint. I hope these rough sketches help to illustrate the idea. Carol Marine graciously shared this method with us at a workshop I attended several years ago. There are mathematical formulas available online that will help you accomplish the same thing, but this one is so much more simple. I don't know about you, but when I sit down to paint, math is the last thing I want to think about!
Have a great Saturday!