Refraction

Lightbeams that come from an object at more than a meters' distance travel parallel through the universe. 

When you look throug a window you will see all objects at the correct size. The parallel lightbeams obviously don't change direction,they don't get "broken." You will understand what this means when you put a stick into a pond…the stick looks broken! 

As a child you probably played with a magnifying glass. You know that through this glass lightbeams can be broken / redirected onto a point (burning point). A magnifying glass is thinner along the edge than the middle, making it a positive glass. The direction of a lightbeam passing through a transparent pobject, such as spectacle glass, changes. The beam is "broken" and a refraction occurs. 

If the beam passes through a glassplate nothing happens. However, if it passes through a bent bit of glass, plastic or other material it changes direction. 

A round lens, thicker in the middle than the edge, forces the lightbeams together (converge). A hollow lens, thinner in the middle than the edge, forces lightbeams apart (diverge). 


A round glass is a "plus" glass. A hollow glass is a "minus" glas.