Derive an expression for equivalent focal length of two thin lenses kept in contact. - Sarthaks eConnect | Largest Online Education Community
When two thin lenses are kept in contact, prove that their combined or effective focal length F is given by 1/F = 1/f1 + 1/f2 where the terms have their usual meaning.
![Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius](https://www.rp-photonics.com/img/focal_length.png)
Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius
![optics - How is focal length defined for a two-lens system, separated by a distance $d$? - Physics Stack Exchange optics - How is focal length defined for a two-lens system, separated by a distance $d$? - Physics Stack Exchange](https://i.stack.imgur.com/fwrwB.png)
optics - How is focal length defined for a two-lens system, separated by a distance $d$? - Physics Stack Exchange
![homework and exercises - Inserting thick lenses into a thin lens system and deducing values - Physics Stack Exchange homework and exercises - Inserting thick lenses into a thin lens system and deducing values - Physics Stack Exchange](https://i.stack.imgur.com/BWJcI.png)
homework and exercises - Inserting thick lenses into a thin lens system and deducing values - Physics Stack Exchange
![a) Determine the 'effective focal length' of the combination of the two lenses in Exercise 9.10, if they are placed 8.0 cm apart with their principal axes coincident. Does the answer depend a) Determine the 'effective focal length' of the combination of the two lenses in Exercise 9.10, if they are placed 8.0 cm apart with their principal axes coincident. Does the answer depend](https://d10lpgp6xz60nq.cloudfront.net/physics_images/U_LIK_SP_PHY_XII_C09_E01_021_S01.png)
a) Determine the 'effective focal length' of the combination of the two lenses in Exercise 9.10, if they are placed 8.0 cm apart with their principal axes coincident. Does the answer depend
![Derivation of Equivalent Focal Length of Combination of two lens separated by distance #kamaldheerya - YouTube Derivation of Equivalent Focal Length of Combination of two lens separated by distance #kamaldheerya - YouTube](https://i.ytimg.com/vi/JTOSQLL93pY/mqdefault.jpg)