Objects between F and lens
Hold a magnifying glass above a page. The alphabets are magnified.
Objects beyond 2F
Now hold it in front of you and look at your friend. Your friend is upside down and appears smaller!
Stand in front of a tree and hold a piece of paper upright in your hand, so that the paper faces the tree. Hold your magnifying glass as if someone wants to read the blank paper (haha!). Then slowly move the magnifying glass away from the paper, towards the tree. What do you see on the paper as you move the magnifying glass?
In the Flash above, F represents focal length.
Real image is an image that can be projected on a screen. Virtual image can not be projected on a screen but can be observed when looking directly at the optics.
If you like a copy of this Flash, get it here!