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## Homework Statement

**1)**

I have five lenses with f=25 placed at distance 50 from each other, what is the focal length of this system?

**2)**

A light source is placed in the focal point of a lens with f=50, at d=600 a lens with f=400 is placed, at the focal point of the second lens the image is captured, what is the magnification?

## Homework Equations

[itex]\frac{1}{A}[/itex]+[itex]\frac{1}{B}[/itex] = [itex]\frac{1}{F}[/itex] is everything, I think...

## The Attempt at a Solution

1) I think the light rays will converge 25 after the last lens because for lens 2 and 4: 1/-f + 1/b = 1/f → b=-∞ so the light is parallel with x-axis after these lenses. For lens 1,3,5: 1/∞ + 1/b = 1/f → b=f so the projection is in the middle and for the last lens 25 away.

2)

I'm thinking the light is parallel to x-axis after the first lens because 1/f +1/b =1/f →

b=∞ and then for the second lens 1/∞ + 1/b = 1/f → image in f, so no magnification has occured.

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It's not certain both of my solutions are wrong, but probably both are :(.

If someone has a link to info about how to calculate lens after lens that would be great, I cant goggle it since I don't know what this sort of problem is called and my book is terrible.no help.

I am very happy for any help I can get, so thanks in advance.