Review Sheets: Lenses

shape

"caved in"

"bowed out"

position of principal focus

F is "behind the lens"
on the opposite side of the lens as the incoming light

F is "in front of the lens"
on the same side of the lens as the incoming light

image
position

1/d_o + 1/d_i = 1/f
do is always positive
d_i is positive if real
d_i is negative if virtual
f is positive (convex)

1/d_o + 1/d_i = 1/f
do is always positive
d_i is always negative (virtual)
f is negative (concave)

image
properties

virtual, upright, M < 1
ray diagrams

d_o Ž Ľ	d_i = -f virtual	M 0
any d_o< Ľ	0 < d_i < -f virtual	M < 1

magnification

M = | d_i / d_o | = | I / O |

rays

#1 top of the object, parallel to the axis, strikes the lens, refracts through F

#2 top of the object, passes through the center of the lens unbent

#3 top of the object, aims for F', strikes the lens, refracts parallel to the axis

#1 top of the object, parallel to the axis, strikes the lens, refracts through F (dot in line to F)

#2 top of the object, passes through the center of the lens unbent

#3 top of the object, aims for F', strikes the lens, refracts parallel to the axis (dot back refracted ray)