PH 103

Dr. Cecilia VogelLecture 9

Review

Outline Multiple Lenses application to microscope and telescope

Lenses more corrective lenses application to magnifier

Angular size and angular magnification

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

MicroscopeEyepiece lens acts like simple magnifier

Meye = N/do Nfeye

Overall magnification multiply the individual magnifications M = -(di/fobj)(Nfeye)

eyeobj

i

ff

NdM

( )eye

obj eye

L f NM

f f

L = tube length

Usually |M| is given

Microscope

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

( )eye

obj eye

L f NM

f f

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?

=very far!

final image

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 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

final image

=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!