A circle seen at an angle looks like an ellipse: a smooth oval, round at both ends. The top of a cup, the bottom of a bucket and a plate on a table are all circles you see as ellipses.
Key idea
An ellipse is thinnest near eye level and rounder the farther it is above or below eye level. It is smooth all the way around, with no points.
Why it works
At eye level you see a plate exactly edge-on, so it is a line. Raise it or lower it and you start to see its face, so the ellipse opens up. The bottom of a cup on a table is farther below your eyes than its top, so you look down on it more steeply, and its ellipse is rounder.
Worked example: A glass on the table
You sit at a table and look at a glass. Which looks rounder: the ellipse at the rim, or the ellipse at the base?
- Both are below your eye level.
- The base is farther below your eyes than the rim.
- Farther from eye level means rounder.
Answer: The base.
Common mistake
People draw the bottom of a cup as a flat line, or give ellipses pointed ends like a football. A circle has no corners, so its ellipse has none either. And the bottom of a cup below eye level is rounder than the top, never flatter.