A simple microscope uses a single lens to magnify objects and forms a virtual image. It provides low magnification and is used to examine things like skin, algae, and soil samples. A compound microscope has two lens systems that provide higher magnification by compounding the magnification of the objective and eyepiece lenses. It allows detailed examination of stained slides and is commonly used in biology labs and medical diagnostics. A stereo microscope uses two separate optical paths and lens systems to provide a three-dimensional view of surfaces. It has lower magnification than compound microscopes and is used for examining things like insects and circuit boards.

1. MICROSCOPY 1
SIMPLE MICROSCOPE
A simple microscope works on the principle that when a tiny object is placed within its
focus, a virtual, erect and magnified image of the object is formed at the least distance of
distinct vision from the eye held close to the lens.
Refer…Magnification*** and Construction - mechanical and optical parts
Working Principle:
Light from a light source (mirror) passes through a glass stage with slide containing a thin
transparent specimen. A biconvex - ocular lens based on its capacity magnifies the size of
the object, resulting in an enlarged virtual image.
APPLICATIONS OF SIMPLE MICROSCOPE
1. Simple microscope is used to obtain small magnifications such as morphology.
2. Simple microscope is usually used for study of microscopic algae, fungi and biological
specimen.
3. Simple microscope is used by skin specialists to scan for various skin disorders.
4. Simple microscope is used to see the magnified view of different particles present in
diverse soil forms.
COMPOUND MICROSCOPE
A compound microscope is an optical instrument used to observe the magnified images of
small objects on a glass slide. Compound microscopes are so called because they are
designed with a compound lens system. The objective lens provides the primary
magnification which is compounded (multiplied) by the ocular lens (eyepiece). It provides
higher magnification and overcomes the limited clarity of image observed by stereo or
other low power microscopes and reduces chromatic aberration. It facilitates detailed
study of specimen in a two-dimensional spatial lane. High-quality Compound
Microscopes are available in Monocular, Binocular, and Trinocular configurations. It has
a series of two lenses; (i) the objective lens (4x, 10x, or 100x) close to the object to be
observed and (ii) the ocular lens or eyepiece(5x-30x), through which the image is viewed
by eye.

2. MICROSCOPY 2
Compound microscopy classified based on the field observed;
1. Bright-field microscopes
2. Dark-field microscopes
1. BRIGHTFIELD MICROSCOPES
 The bright-field microscope is the simplest optical microscope and is popularly
employed.
 The object to be inspected is normally placed on a clear glass slide, and light is
transmitted though the object. This makes the object appear dark against a bright
background, hence the term Bright-field.
WORKING PRINCIPLE
Light from the illumination (light) source from the base of the Microscope stand is
aimed at sub-stage condenser lens. The sub-stage condenser lens focuses light through
slit in the stage onto the sample. The sample absorbs some amount of light based on
stain, pigmentation or thickness. The projected light from the sample is collected by
objective lens and is magnified according to its capacity, creating a primary image. The
primary image is magnified by ocular lens (eye piece), which also act as magnifying glass
by allowing the observer to view virtual and magnified image of the sample.
APPLICATIONS
 Widely used for stained or naturally pigmented or highly contrasted specimens
mounted on a glass microscope slide.
 Used in biology classrooms (mitosis & meiosis, etc.) and clinical laboratories.
 Used in pathology to view fixed tissue sections or cell smears / smears.

3. MICROSCOPY 3
2. DARKFIELD MICROSCOPES
 Used to observe unstained – transparent specimens.
 Samples having very close refractive indices value as that of surroundings are difficult
to observe with conventional bright-field microscopes, such samples are ideal for
observation with dark background.
 Example: small aquatic organisms, oocytes and other thin-transparent materials with
Refractive Index from 1.2 to 1.4
WORKING PRINCIPLE
Light from the illumination (light) source from the base of the Microscope stand is aimed
at dark-field ring. Dark-field ring is an opaque disk blocks the central rays of the light.
The marginal/peripheral light rays are directed to sub-stage dark-field condenser lens.
The specimen on the stage is illuminated only with the peripheral oblique rays. As a
result of this, the field appears dark. The scattered ray from bright specimen is
collected by objective lens and is magnified according to its capacity, creating a primary
image. The primary image is magnified by ocular lens (eye piece), which also act as
magnifying glass by allowing the observer to view virtual and magnified image of the
sample.
APPLICATIONS
 Used for examination of live sample.
 Unstained or lightly stained specimen or fluids could also be observed.
 Useful for diagnosis of disease.
 The bacterial motility can be studied.
 Precious stones are viewed.

4. MICROSCOPY 4
STEREO MICROSCOPE
 The stereo microscope, also called a Dissecting microscope, as it allows the operator
to manipulate/dissect the specimen while it is being observed through the microscope.
 It provides relatively lower magnification usually below 100x.
 They provide a close-up, 3-Dimensional view of objects surface textures.
 Stereo microscopes are used for large biological samples ( insects, leaf, tissues…) and
medical science applications as well as in the electronics industry, such as by those
who make circuit boards or watches.
WORKING PRINCIPLE
The Optical binocular stereo microscope consists of two objective lens and two ocular
lens. Two spatially separated optical path focuses sample on the same point from
slightly different angles. The laterally correct, upright-erect image is obtained.
ADVANTAGES
 They can have a single fixed magnification, several discrete magnifications, or a zoom
magnification system.
 Many stereo microscopes are modular in design.
 It does not require a slide preparation.
 It enables to switch from bright-field to dark-field and vice-versa.