Download microscope, telescope

PH 103
Dr. Cecilia Vogel
Lecture 9
Review
Lenses
more corrective lenses
application to magnifier
Angular size and angular magnification
Outline
Multiple Lenses
 application to microscope
 and telescope
Multiple Lenses
Two lenses -- can do more than cases we
discussed for single lens
 If you use more than one lens, you can
get different results than cases I, II, III.
Just like with mirrors,
You can make an image of an image
with lenses, too.
Multiple Lenses
Making an image of an image with 2 lenses:
The first lens the light goes through
makes the first image.
Then that first image, acts as the “object”
that the second lens will make an image of.
You get a second image, which you see.
If there are more than two lenses,
continue this process
previous lens’ image is next lens’ “object”
Microscope
Two lenses -- can do more magnification
than a simple magnifier can
Compound microscope uses 2 lenses.
 Type of lenses used in microscope:
 two converging lenses
 objective lens is near object
 eyepiece (or ocular) lens is near eye
Microscope
Objective lens is case I
original object is further than f
but near the focal point
 so image is large (Java applet)
So first image
produced by objective lens
is real and inverted and larger
mobj = -di/do  -di/fobj
Microscope
Eyepiece lens acts like simple magnifier
Meye = N/do  N/feye
Overall magnification
 multiply the individual magnifications
 M = -(di/fobj)(N/feye)

di N
M 
M 
f obj f eye
( L  f eye ) N
f obj f eye
L = tube length
Usually |M| is given
Microscope
M 
( L  f eye ) N
f obj f eye
What should you do
to each to make a
stronger microscope?
objective -- shorter fobj
tube length -- make it
longer, so di can be
bigger.
eyepiece -- shorter feye
final image
Refracting Telescope I
Refracting telescope
also uses two
converging lenses
One style is like
microscope,
except the original
object is far away.
The first image is NOT
magnified
makes sense, huh?
final image
=very far!
Image as Real Object
Note that in the
telescope at right, the
first image
which acts as the object
for the second lens
is in front of the
second lens
the object for the 2nd
lens is in front of the
lens, so it is a real object
=very far!
Refracting Telescope I
The image is inverted for this type of
telescope
the original object is real,
and the first image is real,
so the magnification due to the first lens is
–di/do = -(+)/(+)=(-)
Then the 2nd object is real,
and the 2nd image is virtual
so the magnification due to the 2nd lens is
–di/do = -(-)/(+)=(+)
The overall magnification is (-)(+) =(-)
=very far!
Refracting Telescope II
Another style of telescope is like
microscope, except…
the original object is far away,
and the first image becomes a
VIRTUAL object for the second lens
=very far!
Image as Virtual Object
What if the first image
which acts as the object
for the second lens
final image
is behind the second
lens?
the object for the 2nd lens
is behind the lens, so it is
a virtual object
& the object distance is
negative
=very far!
Refracting Telescope II
The image is upright for this type of
telescope
the original object is real,
and the first image is real,
so the magnification due to the first lens is
–di/do = -(+)/(+)=(-)
Then the 2nd object is VIRTUAL,
and the 2nd image is virtual
so the magnification due to the 2nd lens is
–di/do = -(-)/(-)=(-)
The overall magnification is (-)(-) =(+)
=very far!