Optics - Diameter of moon viewed through telescope

[elizabeth9681]

Homework Statement

I've been stuck on this problem for a while now, and have tried it several different ways, but with no results. I'm sure I'm missing something obvious or simply approaching it from the wrong direction.

The moon subtends an angle of 0.5 degrees at the objective lens of a terrestrial telescope. The focal lengths of the objective and ocular lenses are 20 cm and 5 cm, respectively. Find the diameter of the image of the moon viewed through the telescope at near point of 25 cm.

Homework Equations

M = - fo/fe where fo = focal point of objective and fe = focal point of eyepiece

 

[member 553083]

The Attempt at a Solution I've tried to work this problem multiple times, and so far I have come up with the following equation, but I'm not sure if it's correct: M = (20/5) * (25/20) = 1.25 From here, I'm not sure what to do. Any help would be greatly appreciated.