Lens focusing light from two different light sources

[Purplepenguin]

Hello,

question regarding the way convex lenses bend and refocus the light;

will it refocus the light from two different light sources to the SAME point?

OR

will it refocus each light source to a DIFFERENT point?

(please see picture).

thank you!

[exchemist]

1 hour ago, Purplepenguin said:

Hello,

question regarding the way convex lenses bend and refocus the light;

will it refocus the light from two different light sources to the SAME point?

OR

will it refocus each light source to a DIFFERENT point?

(please see picture).

thank you!

If the light sources are at different distances from the lens, then it will focus them at different distances from the lens.

The formula (using the approximation for thin convex lenses) is: 1/f = 1/u + 1/v, where f is the focal length of the lens, u is the distance of the object (light source) from it and v is the distance of the image from it.  

However, at very large values of u,  i.e. when the object is a long way from the lens, 1/u becomes negligibly small, the light rays entering the lens become essentially parallel and then v ~f, irrespective of the actual distance of the object from the lens. So, at such long-range distances, the image is formed at practically the same point regardless of how far way the object is.  

[Purplepenguin]

Hi exchemist,

 

thank you for the explanation