Imagine you're standing, holding a mup of coffee in your hand. When you're holding the mup at waist height and you look down at the mug, you see the top of the mug as a perfect circle. Now bring the mug up to eye level and see how that 'circle' changes shape, becoming flattened out as an ellipse, because you are no longer looking at it from directly above. Now take a look at the curve at the bottom of the mug and you'll see it matches that of the top. (This, of course, presumes that you've a plain coffee mug, not a fancy one.)

In slightly more technical terms, the higher your viewpoint with regard to the object, the closer to a true circle an ellipse will be. Conversely, the lower your viewpoint is, the flatter the ellipse will be. As your viewpoint moves from above a cylindrical object down until you're looking at it side on, so the ellipse flattens out, as shown in the diagram.

In order for a cylindrical object such as a mug, vase, or bottle to look real in a painting, it's crucial that the ellipses are accurate. It's a common beginner's error to have ellipses on an object that are inconsistent, for example the top of the coffee cup is shown as a circle and the base as an ellipse. Or to draw the same ellipse on all the cyndrical objects in a composition, without consideration for viewpoint and what the actual ellipse on each object is.

Take a look at the two cylindrical containers shown here. As your viewpoint moves from the side to the top, note how the ellipses change. Also note how the ellipse at the top and bottom change together as your viewpoint changes. Look too at how the ellipses on the various part of the tomato sauce bottle remain consistent, even though the neck of the bottle is much narrower than the base.

Tips:
• If you draw a horizontal line through the widest point of an ellipses, the back half of the ellipse should be shallower than the front half. This has to do with perspective. Think about how the sleepers on a railway track appear closer and closer together the further away they are, even though you know they're the same distance apart. Similarly, the back half of the ellipse is slightly further away from you, so slightly shallower than the front half of the ellipse.

• An ellipse is not the same shape as a rugby ball, that is it doesn't have sharp or pointed ends, but is a curve.

• If you have trouble seeing ellipses, take a photograph of still life setup composed of various size bottles, tins, and other cylindrical containers then use a broad felt-tip pen to draw the ellipses on the various objects (or scan it into your computer and do it in a drawing program). Or take the felt-tip pen to photos/adverts from magazines with cylindrical objects in them.