# Homework Help: Focal Length

1. Apr 23, 2010

### vucollegeguy

1. The problem statement, all variables and given/known data

a) What is the focal length of the eye-lens system when viewing an object at infinity? Assume that the lens-retina distance is 1.8cm.
b) What is the focal length of the eye-lens system when viewing an object 35cm from the eye? Assume that the lens-retina distance is 1.8cm .

2. Relevant equations

3. The attempt at a solution

I assumed that for part A that 1/inf went to zero but that answer was wrong. I'm not sure How to calculate this. Please help if you can.