If you've ever used a magnifying glass to burn things, it's the same principle. To focus a certain distance, there is a point from a light source where all beams converge. Condenser lenses help to condense the beam to a narrower profile, not necessarily a purely focused spot. I'd love to have a light that throws beams parallel to the light...
A coherent beam?
:devil:
use of aspheric condenser lens is to concentrate all light.
as i saw if all light rays coming parallel then and only then it will give spot of light.
if light rays are little bit inclined then??
will it concentrate all light.
dc38's description of the way you move the magnifying glass in/out to FOCUS the beam...as too far away, vs too close, is NOT as concentrated a beam as when its "just right"....works for me.
For a flashlight, the idea is the same...so for an aspheric lens, you are trying to focus the beam so that a projection of the picture of the LED is projected off into the night.....just like a slide projector image is.
If you take a flashlight (Any one will do...) and hold a magnifying glass in front of the beam, and shine the beam on a wall....if you move the magnifying glass in/out, you will find the distance that puts a picture of the LED on the wall...and, that's how the aspheric lens works.