DETERMINATION OF FOCAL LENGTH OF LARGE FOCAL LENGTH CONVEX LENSES

In the determination of focal length of large focal length lenses, con ventionally, a large length of optical bench is needed to accommodate the experimental set-up, and the measurements are associated with benc h errors. In order to overcome these drawbacks, a simple method is sug gested wherein the use of a plane mirror reduces the required length o f the optical bench by nearly a factor of two and the bench errors are minimized with the use of a travelling microscope for the measurement of distances.