Chapter 23: Images formed by Lenses

Lecture 13

mirrors redirect light rays through

reflection

lenses redirect light rays through

refraction

thin symmetric lenses - there is refraction at 

both interfaces

lenses have 

two focal points, one on each side of the lens and both the same distance from the lens

as with spherical mirrors, the focal points are defined by the

behavior of rays parallel to the principle axis

converging lenses:

positive focal length

diverging lenses:

negative focal length

a converging lens is

thicker at is center than at its edges

converging lens - if the object is far away from the lens (relative to the focal point), the image is 

real and inverted 

converging lens - if the object is close to the lens (relative to the focal length), the image is

virtual and upright 

the object distance is positive if

the object is on the side of the lens from which the light is coming, and negative otherwise

the image distance is positive if

the image is on the opposite side of the lens from which the light is coming (real image), and negative otherwise (virtual image)

the height of the image is positive if the image is 

upright and negative if the image is inverted

a biconvex (converging) lens is the type of lens in

the human eye, and it is responsible for forming images

with normal vision, light focuses precisely on

the retina at a location called the focal point of the eye lens

eye lens - the image is

• real (on the opposite side of the object)

• inverted 

• diminished 

through years of evolution, the brain has learned to intercept the

inverted retinal image as an upright perception of the external world

a diverging lens is

thinner at its center than at its edges

a diverging lens produces only one type of image

always virtual, diminished, and upright

so converging (convex) lenses act like

concave mirrors and diverging (concave) lenses act like convex mirrors