An optical instrument employed for angular magnification contains an objective of 25 D and an eyepiece of 20 D . When the eye is least strained, the tube length is 25 cm . What is the angular magnification produced?

Step-by-step solution

Given the power of the objective lens, P_o = 25 D , its focal length is: f_o = 100 P_o = 100 25 = 4 cm Given the power of the eyepiece, P_e = 20 D , its focal length is: f_e = 100 P_e = 100 20 = 5 cm For the eye to be least strained, the final image must be formed at infinity. This requires the intermediate image formed by the objective to lie exactly at the first focal point of the eyepiece. Thus, the object distance for the eyepiece is: u_e = f_e = 5 cm The tube length L of the microscope is the distance between