Editor-in-Chief : V.K. Rastogi

Volume 31 | No 1 | January 2022 |

A Special Issue in the Memory

of

Late Prof B N Gupta

Guest Edited By : R S Sirohi & A K Nirala

Anita Publications

FF-43, 1st Floor, Mangal Bazar, Laxmi Nagar, Delhi-110 092, India

Asian Journal of Physics Vol. 31 No 1, 2022, 1-16

**On the methods to determine the focal length of an imaging system: A tutorial approach**

Rajpal S Sirohi

Alabama A&M University Normal, Alabama, USA

This article is dedicated to late Prof B N Gupta

Focal length of an imaging system is an important parameter as it determines its gathering power, numerical aperture and resolution. Its determination becomes very difficult as one of the planes is not physically accessible. A number of methods have been developed that measure either the effective focal length or the back focal length. The objective of the present paper is to discuss various methods that have been investigated and reported in the literature. © Anita Publications. All rights reserved.

Keywords: Focal length, Radius of curvature, Nodal slide, Interferometry.

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