diff between focus and principal focus.?
Answers
Principal focus is a point (on the principal axis) where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses). ... Principal Focus also determines the focal length of the lens/mirror. Focus is just a random point where some rays meet, it might be at the principal focus or otherwise.
Principal focus is a point (on the principal axis) where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses). It is a fixed point of particular lens/mirror and depends upon its shape. Principal Focus also determines the focal length of the lens/mirror.
Focus is just a random point where some rays meet, it might be at the principal focus or otherwise. It also need no be placed on the principal axis of the lens/mirror.