Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
 Measuring:
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Topics
Focal lengths of thin lenses
Real image magnification
Virtual image magnification (simple magnifier)
Compound microscope magnification
Size of an unknown object
Astronomical telescope magnification
Entrance and exit pupils of telescope
 Theory:
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•
•
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The lens formula
Transverse magnification
Magnifier magnification
Compound microscope magnification
Telescope magnification
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Thin Lens
yo
Fo
Fi
yi
xo
f
so
Lensformula:
1 1 1
 
s0 si f
xi
f
si
T ransverseMagnification :
si
yi
MT 

so
yo
Quantity
so
si
f
yo
yi
Sign
+
-
Real object
Real image
Converging lens
Erect object
Erect image
Virtual object
Virtual image
Diverging lens
Inverted object
Inverted image
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Measuring focal length of converging lens
Object at “infinity”  Image appears at focal point
Lens
Lamp at front desk
Screen:
Image of
lamp
Object at so  Image at si  Use lens formula to get f
Your lamp
from optics
set
in metal
holder
Reticule
Lens
Screen:
Image of
reticule
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
The Magnifying Glass
au 
yo
au
yo
do
do : near pointof eye
Eye
do
aa 
yi
F
u : unaided
yo
yi
L
aa
so
si
L
l
Eye
a : aided
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
The Magnifying Glass
aa 
yi
F
yo
yi
L
a : aided
aa
l
so
Eye
si
L
MagnifyingPower: M p 
M
so 
a a yi d o
y d
 
 i o
au
L yo
yo L
yi
s
 i
yo
so
si f
(fromlens formula)
si  f
yi
s
s
  s if  1  i
i
yo
f
s f
i
si  l  L  si   L  l 
Mp 
do
L
 L l 
1 

f 

Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Mp 
do
L
 L l 
1 

f 

The Magnifying Glass
Special Cases:
Eye as close as possible to the lens to maximize Mp:
l0
 L  do do
1   

l 0
f
L
f


WhenL  d o : M p is maximized(if any closer theimage can't be focused on any more)
 
 Mp


M 
p l 0
do
L
 1
Relaxed Viewing:
 
 Mp
do
25cm
 1
f
f
so  f  si    L  
do

relaxed viewing
L
 L  l  d o do L  l do 25cm
1 
 



f
L
f
L
f
f


Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Measuring Magnification of Magnifying Glass
f
Lens
Reticule
linear graph
paper
Stage Mount
your
eye (close
to lens)
 25 cm
•
•
Move the reticule so it is in focus.
Compare the size of the reticule spacing (1mm) seen through the lens
with the size of the graph paper on the screen (seen simultaneously with the
other eye and not through the lens). See next page for illustration.
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Compare:
3.5 divisions
on the graph paper
taped to the screen
= 1 division on the
Reticule spacing seen
through the lens.
M=3.5
(in this example)
Graph paper 1mm
spacing 25 cm
away from eye:
seen directly
Reticule 1mm
spacing seen
through lens
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
The Compound Microscope
Eyepiece
Eye
Objective
xi
fo
yo
fe
F
F
so
Mo  
si
si
x
 i
so
fo
yi
(T ransv.objectivemagnif.)
M Microscope
s 25cm
x 25cm
 Mo  Me   i 
 i 
so
fe
fo
fe
Virtual image at infinity when
adjusted for relaxed viewing
Me 
25cm
fe
(Eyepiece
magnif.for relaxedviewing)
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Setting up the Microscope Part 1: Getting si , so and thus Mo
Stage mount with screen
Lens A
(Objective)
Reticule
Lamp
 5 cm
 23 cm
•
•
Move lens A back/forth until you get a sharp image of reticule on the screen
Determine si and so and calculate Mo.
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Setting up the Microscope Part 2: Add eyepiece
Lens B
(Eyepiece)
Stage mount with
screen used to be here
(remove)
Lens A
(Objective)
Reticule
your
eye (close
to lens)
fe
•
•
•
Insert lens B, remove stage mount.
Adjust lens B until you see a sharp reticule through the microscope.
Knowing fe compute the total magnification of the microscope.
Lamp
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Setting up the Microscope Part 3: Measure Magnification
Lens A
(Objective)
Lens B
(Eyepiece)
Reticule
Lamp
your
eye (close
to lens)
 25 cm
•
Graph paper for comparison
Compare the size of the reticule spacing (1mm) seen through the microscope
with the size of the graph paper on the screen (seen simultaneously with the
other eye and not through the lens).
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Building a Measuring Microscope
Lens B
(Eyepiece)
Stage mount with screen
used to be here (replace
with Reticule). Move
until in focus
your
eye (close
to lens)
Lens A
(Objective)
Reticule used to be
here (replace with
stage mount and
“unknown object”
obtained from TA).
Move object until it is
in focus.
fe
•
•
•
•
Leave lens A and B where they are.
Adjust object and reticule position until they are both in focus.
Reticule is now where the first real image appears  Both reticule and image of
object can be seen in focus and compared to each other.
Careful when determining the size of the unknown object:
o Reticule only experiences eyepiece magnification.
o Object experiences eyepiece AND objective magnification.
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Astronomical Telescope: Viewing Objects at Infinity
 fo + fe
virtual image
eye
si  f o
eyepiece
 fe
so   (looking at far away objects)
objective
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
from virtual image
Astronomical Telescope: Magnification
aa  
yi
fe
au 
yi
fo
yi
aa
au
si  f o
yo
fo
 fe
MagnifyingPower  MP 

yi
aa
fe
f

 o
yi
au
fe
fo
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Setting up the Telescope and Measuring Magnification
lamp
Lens E
(Eyepiece)
Lens D
(Objective)
your
eye
 fD+fE
•
•
Scale on
white board
at the front of
the room
Look at scale with one eye through telescope and with the other eye directly.
Compare the line spacing to determine magnification.
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
What you should see
white board
telescope eyepiece
Compare scale seen through
telescope with scale seen
directly to determine M.
Here: Magnification looks like M  2.3
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Astronomical Telescope: Measuring the Entrance Pupil
Entrance pupil = diameter of
objective lens = dentrance
Eyepiece Lens
Objective Lens
Modern Optics Lab
Lab 3: Experiments with the Telemicroscope
Astronomical Telescope: Measuring the Exit Pupil
(Use a screen to capture a sharp image of the objective lens)
Exit pupil = diameter of focused image
of objective lens = dexit
Diffuse Light
Eyepiece Lens
d exit d entrance

fe
fo
Objective Lens

d entrance f o

 MagnifyingPower
d exit
fe