Converging lens?

Question

A movie camera has a converging lens with a focal length of 88.0 mm. It takes a picture of a 169 cm tall person standing 15.6 m away. What is the height of the image on the film?

Answer 1

The simplest equation makes use of the "thin lens assumption", which may be iffy when applied to an expensive multielement movie lens. But here it is. From the ref., 1/FL = 1/Di + 1/Do, where FL is focal length, Do is object distance and Di is the image distance.
First you use the above equation to find the distance from the lens to the image. Then the ratio of the object and image sizes is the same as the ratio of their distances.
1/Di = 1/FL - 1/Do
Di = 1 / (1/0.088 - 1/15.6)
Then Si (image size) = So (object size) * Di / Do.
I get about 10 mm.