1. The image produced by one lens serves as the object for the next lens.
Lenses in Combination
The image produced
by one lens serves as
the object for the next
lens.

2. eyeball: sphere with a ~ 25 mm.
The Human Eye
n=1.34
n=1.38
n=1.33
eyeball: sphere with a ~ 25 mm.
Cornea: membrane covers the aqueous humor (liquid)
iris: colored portion of the eye and controls the amount of light that enters
pupil: opening in the iris, diameter 2-7 mm (dilates in dim light, contracts in bright light)
the lens: flexible, shape controlled by the ciliary muscle.
Inside: jelly-like substance (the vitreous humor)
Retina: light-sensitive part of the eye, consisting of millions of structures called rods and cones.
From the retina, electrical impulses are sent to the brain via the optic nerve
Finally the brain interprets the image.

3. Focal length accommodates to form a sharp image at the retina
The Human Eye
Focal length accommodates to form a sharp image at the retina
The lens only contributes about 20-25% of the refraction, but its function
is important.

4. NEARSIGNTEDNESS objects beyond the “far point” can’t be seen sharply
The Human Eye
NEARSIGNTEDNESS
objects beyond the “far point”
can’t be seen sharply
object for the second (eye) lens
The lens creates an image of the distance object at the far point
of the nearsighted eye.

5. Example 12 Eyeglasses for the Nearsighted Person
The Human Eye
Example 12 Eyeglasses for the Nearsighted Person
A nearsighted person has a far point located only 521 cm from the
eye. Assuming that eyeglasses are to be worn 2 cm in front of the
eye, find the focal length needed for the diverging lens of the glasses
so the person can see distant objects.

6. The Human Eye

7. FARSIGNTEDNESS objects closer than the “near point”
The Human Eye
FARSIGNTEDNESS
objects closer than the “near point”
can’t be seen sharply
object for the second (eye) lens
The lens creates an image of the close object at the near point
of the farsighted eye.

8. THE REFRACTIVE POWER OF A LENS – THE DIOPTER
The Human Eye
THE REFRACTIVE POWER OF A LENS – THE DIOPTER
Optometrists who prescribe correctional lenses and the opticians
who make the lenses do not specify the focal length. Instead
they use the concept of refractive power.

9. Angular Magnification and the Magnifying Glass
The size of the image on the retina determines how large
an object appears to be.
Same angle apparently have the same size

10. Angular Magnification and the Magnifying Glass
for small angles

11. Angular Magnification and the Magnifying Glass
Example 14 A Penny and the Moon
Compare the angular size of a penny held at arms length with that of
the moon.
Penny
Moon
the penny looks larger than the moon

12. Angular Magnification and the Magnifying Glass
increases the angle
the angle can be increased without a glass, moving
the object closer to the eye. But the closest position is N
(near point)
Angular magnification
with glass
without glass
Angular magnification
of a magnifying glass

13. Angular Magnification and the Magnifying Glass
increases the angle
the angle can be increased without a glass, moving
the object closer to the eye. But the closest position is N
(near point)
If di=-N (closest distance)

14. Angular Magnification and the Magnifying Glass
increases the angle
the angle can be increased without a glass, moving
the object closer to the eye. But the closest position is N
(near point)
If di=infinite (eye is relaxed)
For best M the image is at N
f has to be very small

15. The Compound Microscope
To increase the angular magnification
beyond that possible with a magnifying
glass, an additional converging lens
can be included to “premagnify” the
object.
magnifying glass L
Angular magnification of
a compound microscope

16. Optical Instruments, Compound Microscope
Fig
O close to F1
I close to F1’
do~fo
Mag. Lens
fo<<s
s=L-fe-fo~L-fe
(34-18)

17. Angular magnification of an astronomical telescope
The Telescope
Angular magnification of
an astronomical telescope

18. Optical Instruments, Refracting Telescope
I close to F2 and F1’
Mag. Lens
first image (real inverted) formed at Fo
Fe and Fo coincide
Final image is at infinity
L=fob+fey
fob>>fey