 

Topics

Measuring:

• 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:

• The lens formula • Transverse magnification • Magnifier magnification • Compound microscope magnification • Telescope magnification

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

y o F o

Thin Lens

F i y i

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Lens formula : 1

s

0 

1

s i



1

f

x o s o f f s i x i

Transverse Magnificat ion :

M T



s i s o



y i y o

f s o s i y o y i

Quantity +

Real object Real image Converging lens Erect object Erect image

Sign -

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

Lamp at front desk Lens Screen: Image of lamp 

Object at s

o 

Image at s

i 

Use lens formula to get f

Your lamp from optics set in metal holder Reticule Lens Screen: Image of reticule

y

o

y

i

F

a u

d

o

s

i

y

o

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

The Magnifying Glass

a

u



y d o o

u : unaided d

o

: near point of eye

Eye

a

a



y i L

a : aided

s

o l a a

Eye L

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

y

i

F y

o

The Magnifying Glass

a

a



y i L

a a

s

o l

s

i Magnifying Power :

M p



L

a a

a u



y i L



d o y o



y y o i



d o L

Eye

s i



l



L

 a : aided

s i

  

L



l



M



y i y o

 

s s o i s o



s i s i



f f

(from lens formula)

y y o i

 

s i s i s i



f f

 1 

s i f M p



d o L

  1 

L



l f

 

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

M p



d o L

  1 

L



l f

 

The Magnifying Glass Special Cases:

 Eye as close as possible to the lens to maximize M p :

l

 0 

p l

 0 

d o L

  1 

L f

  

d o L



d o f

When L  d o :   

p l

 0 

M p

is maximized 1 

d o f

 1  25

cm f

(if any closer the image can' t be focused on any more)  Relaxed Viewing:

s o



f



s i

  

L

    

p

relaxed viewing 

d o L

  1 

L



l f

  

d o L



d o f L



l L



d o f

 25

cm f

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Measuring Magnification of Magnifying Glass

Lens

f

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.

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)

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope Graph paper 1mm spacing 25 cm away from eye: seen directly Reticule 1mm spacing seen through lens

Objective y

o F

s

o

The Compound Microscope

f

o F

s

i

x

i

f

e

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Eyepiece Eye

M o

 

s s o i

 

f x i o

(Transv.

objective magnif.)

y

i

M Microscope



M o



M e

 

s s o i

 25

cm f e

 

f x i o

 25

cm f e

Virtual image at infinity when adjusted for relaxed viewing

M e

 25

cm f e

(Eyepiece magnif.

for relaxed viewing)

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Setting up the Microscope Part 1: Getting s i , s o and thus M o

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 s i and s o and calculate M o .

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Setting up the Microscope Part 2: Add eyepiece

Lens B (Eyepiece) your eye (close to lens) Stage mount with screen used to be here (remove) Lens A (Objective) Reticule Lamp 

f

e • • • Insert lens B, remove stage mount.

Adjust lens B until you see a sharp reticule through the microscope.

Knowing f e compute the total magnification of the microscope.

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Setting up the Microscope Part 3: Measure Magnification

Lens B (Eyepiece) your eye (close to lens) Lens A (Objective) Reticule Lamp  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 Lens B (Eyepiece) your eye (close to lens)

Building a Measuring Microscope

Stage mount with screen used to be here (replace with Reticule). Move until in focus 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.



f

e 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

 f o + f e virtual image eye eyepiece  f e s i  f o objective s o   (looking at far away objects)

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope from virtual image

Astronomical Telescope: Magnification

a

a

 

y i f e

a a y i a

u



y i f o

s i  f o f o  f e Magnifying Power 

MP

 a a

a u

 

y i y i f o f e



f o f e

a u y o

Modern Optics Lab

Lab 3: Experiments with the Telemicroscope

Setting up the Telescope and Measuring Magnification

lamp your eye Lens E (Eyepiece) Lens D (Objective)  f D +f E 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.

What you should see Modern Optics Lab

Lab 3: Experiments with the Telemicroscope 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 = d entrance 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 = d exit Diffuse Light Eyepiece Lens Objective Lens

d exit f e



d entrance f o



d entrance d exit



f o f e

 Magnifying Power