# Optics - Lens

1. Mar 19, 2014

### luiseduardo

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

Two converging lenses of the same focal length f are separated by distance 2f. The axis of the second lens is inclined at angle θ = 60º with respect to the axis of the first lens. A parallel paraxial beam of light is incident from left side of the lens. Then:

(A) Final image after all possible refraction will formed at optical centre of first lens
(B) Final image after all possible refraction will formed at optical centre of second lens
(C) Final image after all possible refraction will formed at distance f from second lens
(D) Final image after all possible refraction will formed at distance f from first lens

2. Relevant equations

f = p.p'/p+p'

3. The attempt at a solution

Here the solution:

But, I don't agree with this line:

f/x = cos 60, but I think the correct is x/f = cos 60, so x = f/2. But the answer is 2f. Anyone could see if i'm wrong ?

2. Mar 20, 2014

### ehild

You are right, the first image is at f/2 distance from the second lens.

ehild

3. Mar 20, 2014

### Simon Bridge

Check by tracing out a ray diagram - the image from the first lens is the object for the second.
You can also see how your course notes tell you to treat the situation when a lens is tilted.

4. Mar 20, 2014

Thanks man.