Compound Microscope

Hans Lippershey

Zaccharias Hanssen

Hans Lippershey

Zaccharias Hanssen

A compound microscope is a

microscope with two or more convex

lenses.

A light source is used to illuminate

what is being observed.

There are usually four objective lenses

with magnifications of 4X, 10X, 40X,

and 100X.

Head

Arm

Base

Eyepiece

Fine Adjustment Knob

Coarse Adjustment Knob Stage

Illuminator

Objectives

Revolving Nosepiece

Diaphragm

Lenses

• composed of two lenses:

objective = short focal length

eyepiece = focal length of few cm

• lenses separated by some distance greater

than either lens' focal length

How does it work?

• object placed outside the focal length of

objective, forms inverted image near focal

length of eyepiece

• eyepiece magnifies the image

• the lenses of a compound microscope

bend the light that you shine from the

bottom through the sample to make it

seem larger. there are two lenses to add

to (compound) the effect

Image Formation

•The object (O) is placed just outside Fo, the principal focus of the objective lens.

•Fe is the principal focus of the eye lens.

•A real, inverted magnified image I1 is formed. The magnified image I1 acts as an object for the eye lens.

•The final image I2 is virtual and is magnified still further. It is inverted compared with the object.

I2 may appear 1000 times larger than the object.

Magnifying Power

Definition:

Magnifying Power

-the ratio of the size of the final image (I2) as seen through the

microscope to the size of the object as seen with a naked eye.

Physics behind… Magnification produced by the objective is given by:

Mo= size of image / size of object

Mo= q1/ p1--------------- (1)

Magnification produced by the eye piece is given by:

Me= size of image / size of object

Me= q2/ p2

Me= d / p2--------------- (2)

Using thin lens formula for eye piece :

1/f2 = 1/q2 + 1/p2

Here f2 = fe, q2 = - d and p = p2

1/fe = 1/-d + 1/p2

1/fe = -1/d + 1/p2

Multiplying both sides by "d"

d/fe = -d/d + d/p2

d/fe = -1 + d/p2

1 + d/fe = d/p2

d/p2 = 1 + d/fe----------------(3)

Comparing equation (2) and (3)

Me = 1 + d/fe--------(4)

Total Magnification:

M =Mo X Me

M = (q1/p1)(1 + d/fe)

In order to get maximum magnification, we must decrease p1 and increase

q1 .Thus maximum possible value of p1 is fo i.e p = fo and maximum possible

value of q1 is the length of microscope i.e q1 = L

Therefore the magnification produced by a compound d microscope is

given by:

M = (L/fO)(1 + d/fe)

Sources

• http://www.wisegeek.com/what-is-a-compound-microscope.htm

• http://www.microscope.com/compound-microscope-history-t-4.html

•Serway

fin. \:D/