An optical illusion tricks a viewer's mind into believing that something is true when it is not. It uses contrasting lines to trick a viewer's perception and make them think that lines are moving, angled or curved. Alternately, optical illusions can change the way a viewer understands scope or size. With practice, you can create elaborate optical illusions but smaller, easier ones help you practice and develop your technique. A well-crafted optical illusion helps you demonstrate the way your mind interprets the things you see such as making straight lines seem curved.
Draw a diamond in the centre of your paper, using a ruler to keep the lines straight and each line three inches long. Redraw your diamond with longer or shorter sides, If the diamond seems too small or large. Draw the lines thick and dark but make sure to keep them straight.
Set the point of your compass to the centre of your diamond and extend your compass until your pencil is against the side of your diamond. Use your compass setting to draw a circle, connecting each of the sides of your diamond with your circle. Keep your circle lighter than the lines you drew for your diamond.
Set your compass to 1/2-inch less than its current setting and place the point at the centre of your diamond. Draw a circle in the centre of your diamond. Keep the circle lighter than the lines of your diamond.
Change your compass to 1-inch larger than its current setting and place it in the centre of your diamond. Draw another circle around your original one. Repeat this process, drawing additional circles, each at a 1/2-inch larger radius from the last. Keep each line thinner than the lines that make up the sides of your diamond.
Look at your optical illusion and pay attention to the way the circles on your paper appear to skew the lines of your diamond inward. Repeat this process using larger circles and smaller circles and get a feel for the way you can manipulate the way your mind interprets the image you see.
Test your optical illusion by showing it to someone else and asking him to describe the diamond shape in the centre of your page. Ask him if the lines of your diamond are straight or curved inward. See if you can trick people into believing that the lines are curved.