Image Formation in Lens

In order to draw the image formed by any lens, only two rays are required.

1. A ray parallel to the principal axis of the lens converges after refraction at the principal focus of convex lens. It appears to diverge off in the case of concave lens.

2. A ray towards the optical centre falls on the lens symmetrically and after refraction passes through it undeviated.

lens images 

All these images formed for different positions of object and nature of the image can be summarized as:

# Object Position Image Position Nature Size
  Convex Lens      
1 Between P & F In front of lens Virtual & Erect Larger
2 At F At infinity Real & Inverted Enlarged
3 Between F & 2F Beyond 2F Real & Inverted Larger
4 At 2F At 2F Real & Inverted Same size
5 Beyond 2F Between F & 2F Real & Inverted Smaller
6 At infinity At F Real & Inverted Diminished
  Concave Lens      
7 Anywhere Between P & F Virtual & Erect Smaller