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.
All these images formed for different positions of object and nature of the image can be summarized as:
|#||Object Position||Image Position||Nature||Size|
|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|
|7||Anywhere||Between P & F||Virtual & Erect||Smaller|