Why doesn't a biconvex lens cancel itself out and not change the light beam?

[theonlywalks]

When you have a biconvex, i.e. two convex lens' back to back, doesn't the light beam just come out straight?

Since one convex lens is back to back with another, essentially it is a convex lens, followed by a concave lens. The light would first hit the convex lens, and the light would converge. Then the light would hit the concave lens, and the light would diverge.

This is what happens when the light ray hits each of these independently, yet for some reason when they are back to back (i.e. a biconvex lens) the light gets super converged.

I would think that the light would converge, then it would diverge, and thus be back to what it was originally.

If you take a convex lens and it converges the light coming onto it, then if you flip the lens so the light is coming in the opposite side, the light would diverge would it not?

 

[theonlywalks]

really, no one knows the answer lol?

 

[Bob S]

Open this lens simulation program from the University of Colorado

http://phet.colorado.edu/en/simulation/geometric-optics

and click on the green RUN NOW box in the lower right. Adjust the lens curvature, diameter, and index of refraction.

Bob S

 

[sophiecentaur]

When you have a biconvex, i.e. two convex lens' back to back, doesn't the light beam just come out straight?

Since one convex lens is back to back with another, essentially it is a convex lens, followed by a concave lens. The light would first hit the convex lens, and the light would converge. Then the light would hit the concave lens, and the light would diverge.
etc

You only have to look at any simple lens / ray path diagram to see that you can't possibly be right. What 'cancelling out effect' is there? If you turn right then turn right again, you don't end up going straight!
If in doubt look at Google / Wikkers