All Problems Photometry and Geometrical Optics
Problem 5.54
A telephoto lens consists of two thin lenses, the front converging lens and the rear diverging lens with optical powers \(\Phi_{1}=\) \(=+10 \mathrm{D}\) and \(\Phi_{2}=-10 \mathrm{D}\). Find: (a) the focal length and the positions of principal axes of that system if the lenses are separated by a distance \(d=4.0 \mathrm{~cm}\) (b) the distance \(d\) between the lenses at which the ratio of a focal length \(f\) of the system to a distance \(l\) between the converging lens and the rear principal focal point is the highest. What is this ratio equal to?
\(5.54 .\) (a) The optical power of the system is \(\Phi=\Phi_{1}+\Phi_{2}-\) \(-d \Phi_{1} \Phi_{2}=+4 \mathrm{D},\) the focal length is \(25 \mathrm{~cm} .\) Both principal planes are located in front of the converging lens: the front one at a distance of \(10 \mathrm{~cm}\) from the converging lens, and the rear one at a distance of \(10 \mathrm{~cm}\) from the diverging lens \(\left(x=d \Phi_{2} / \Phi\right.\) and \(\left.x^{\prime}=-d \Phi_{1} / \Phi\right)\) (b) \(d=5 \mathrm{~cm} ;\) about \(4 / 3\)