Sunday, May 21, 2006

9

Focal Points





Click on image to enlarge.

The primary focal point (F1) of a lens is also called the Object-Space Focus.
  • For a plus lens, this is the point from which light must originate to emerge parallel from the lens. Thus, the image is at infinity.

  • For a minus lens, this is the point towards which the incident light must be directed in order for the image rays to emerge parallel.



The primary focal length, (f1), is the distance from the optical surface to the primary focal point (F1). Secondary focal point (F2) of a lens is also called the Image-Space Focus.

  • For a plus lens, this is the point where parallel rays from a distant point object are rejoined to form an image at that point. When parallel rays enter the optical surface, they will focus at the secondary focal point.

  • For a minus lens, this is the point from which diverging rays seem to come from, after a parallel bundle of rays are refracted by a negative lens.



The secondary focal length, (f2), is the distance from the optical surface to the secondary focal point (F2).

  • For a plus (+)/convergent lens, the secondary focal point is to the right of the lens.

  • For a minus (-)/divergent lens, the secondary focal point is to the left of the lens.

0 Comments:

Post a Comment

<< Home