First, we need to find the angle deflection of light ray if it passes a convex lens.


By using lens equation,

we can get

If the lenses are separated by angle of θ, then the total number of lenses is

If we want to trap a ray of light, we just need to have the light forms a (nearly) circle path. On one cycle of the path, the light passes N lenses, so the total deflection is

The total deflection must equal to ,

In order to get the longest focus length, variable h must be at its maximum value (i.e. aperture length, D)

That's my solution.
If you have any question, correction, or comment, please leave a comment below.
Thank you.

Solution - Trapping LensesSocialTwist Tell-a-Friend


Sebastian said... @ March 26, 2009 at 3:40 AM

The maximum value of h is D/2, so the final result is half the one given in the above solutin

ANISH said... @ July 26, 2009 at 10:47 PM

If the angle of deviation becomes 2pi then how will the paraxial approximation hold true. If paraxial approximation fails then we cannot use the general lens equation 1/f = 1/V + 1/U.

Post a Comment