College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 53

A microscope has an objective lens with a focal length of 16.22 mm and an eyepiece with a focal length of 9.50 mm. With the length of the barrel set at 29.0 cm, the diameter of a red blood cell's image subtends an angle of 1.43 mrad with the eye. If the final image distance is 29.0 cm from the eyepiece, what is the actual diameter of the red blood cell Hint: To solve this question, go back to basics and use the thinlens equation.