# Combination lens

1. Oct 10, 2011

### lacrosse1440

Blanking quite a bit on this one

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

Assuming that paraxial light from a distant object enters lens 1, find the image distance s′2 (due to the refraction at lens 2) as a function of the lens separation d. Your answer will also contain f, the unspecified focal length of the converging lens.
2. Relevant equations

f1=f
f2=-2f

3. The attempt at a solution

s'1 = s1f1/(s1-f1)
s2 = d-s'1
s'2 = s2f2/(s2-f2)

But what is s1 since it has to be in terms of f and d? Is s'1 = f since it's a distant object?

But then that would make s1 = infinity, and we are asked to find

"Suppose the camera is trained on a distant object of angular size α radians (α << 1) when viewed by the unaided eye. What is the lateral size y′ on the CCD array of the image of that distant object produced by the zoom lens? Your result will contain d, f and also α."

and

"Effective focal length of the zoom lens: If the camera is fitted with a simple converging lens of focal length F, that distant object would produce an image on the CCD array of lateral size equal to αF. Set the (magnitude of) your result of (d) equal to αF to determine the ”effective focal length” F of the zoom lens as a function of d and f. Work out expressions for F at d = 0 and d = D in terms of f"

Which wouldn't make sense if the magnification is 0. (-s'2/s = 0)