Thin lenses - power, imaging, lateral mag

thin lenses

-ignore the effect of thickness on lens power
-central thickness is small in relation to radii

2 curved refracting surfaces (front and back) connected together

the index of the lens is generally higher than the surrounding media

lens power

sum of both surface powers
Ft= F1 + F2

Lens designs

convex, positive, converging, or plus lenses
-thicker center, thinner edge
concave, negative, diverging or minus lenses
-thinner center, thicker edge
opthalmic lenses: usually meniscus
-minimizes off axis (peripheral) aberrations

lenses have spherical surfaces

biconvex lens
- r1 is + and F1 is +
- r2 is - and F2 is +
biconcave lens
- r1 is - and F is -
- r2 is + and F2 is -

focal lengths

f' is image distance with the object at infinity
f is the object distance with image at infinity

refraction occurs in _____

a single plane
we assume this

focal lengths

F is the primary focal length and
F' is the secondary focal length

Thin lens imaging

-the same as for curved surfaces
-F is now the power of the whole lens instead of just one side
- we can assume that it has air on either side unless otherwise specified

Thin lens imaging formula and relationship

- as RO moves from infinity to primary focal point (F), RI moves from secondary focal point (F') to infinity
- if RO is inside primary focal point (F), a VI is formed
- L'= L + F

focal length formula

f=-n/F
f'= n'/F

extended objects and lateral magnification

- can examine orientation and size of image compared to the object
- typically an arrow extending perpendicular to axis
- point source at tip of the arrow

Lateral magnification (LM) formula

LM= h'/h = l'/l = L/L'

what does LM tell us

-if LM+, image is erect
-if LM-, the image is inverted
-if LM>1, image is larger than object (h'>h)
-if LM

lateral magnification and symmetrical planes

symmetrical planes means LM = -1
if LM =-1, the l=2 f and l'=2f'

plus lens and distant object

- can't really find the lateral magnification because we need the image size or object size
- there is a special case when an object is at infinity