Our eyes cannot focus on objects nearer than about 25 cm or 10 inches. We overcome this limitation by using a convex lens as a simple magnifier (or microscope) and holding it close to the object. Medical science deals with too small object like micro organisms, human body tissue and cells that they cannot be seen distinctly with the unaided eye, the microscope is essential.

What is microscope?

Microscopes are essential instrument in scientific research, medical diagnostics, education, and various industries.  It allows us to examine too small objects, e.g., microorganisms, blood cells, etc., that we cannot see distinctly with the naked eye.

Microscopes give the viewer enhanced magnification (the ability to see small objects), contrast (the ability to identify various parts of the object based on color or intensity), and resolution (the ability to see two neighboring objects as distinct objects).

The human eye can resolve objects of the order of 0.1 mm, while the light microscope can resolve objects on the order of 0.2 μm (200 nm) with a magnification of 1000. The transmission electron microscope can resolve objects on the order of 0.1 nm (100 A ˚ unit.

Microscope lecture slide pptx,

History of microscope

• 1000AD – The first vision scope was invented (inventor unknown) called a readingstone. It was a glass sphere that magnified when placed on top of reading materials.
• 1284 – Italian, Salvino D’Armate is credited with inventing the first wearable eyeglasses.
• 1590 – Two Dutch eyeglass makers, Zaccharias Janssen and son Hans Janssen tested with multiple lenses placed in a tube. They observed that observed objects in front of the tube seemed greatly enlarged.
• 1674 – Anton van Leeuwenhoek father of microbiology built a simple microscope with only one lens to study blood, yeast, insects and many other tiny objects.
• 1830 – Joseph Jackson Lister: reduces spherical aberration or the “chromatic effect” by showing that several weak lenses used together at certain distances gave good magnification without blurring the image. This was the prototype for the compound microscope.
• 1872 – Ernst Abbe wrote a mathematical formula called the “Abbe Sine Condition”. His formula provided calculations that allowed for the maximum resolution in microscopes possible.
• 1903 – Richard Zsigmondy developed the ultra-microscope that could study objects below the wavelength of light. He won the Nobel Prize in Chemistry in 1925.
• 1932 – Frits Zernike invented the phase-contrast microscope that allowed for the study of colorless and transparent biological materials for which he won the Nobel Prize in Physics in 1953.
• 1931 – Ernst Ruska co-invented the electron microscope for which he won the Nobel Prize in Physics in 1986. Electron microscopes make it possible to view objects as small as the diameter of an atom.
• 1981 – Gerd Binnig and Heinrich Rohrer invented the scanning tunneling microscope that gives three-dimensional images of objects down to the atomic level. Binnig and Rohrer won the Nobel Prize in Physics in 1986.

Types of microscope

1. Compound Microscope

Compound microscopes are light illuminated. The image seen with this type of microscope is two dimensional. This microscope is the most commonly used in biological labs. You can view individual cells, even living ones. It has high magnification up to 1000x. However, it has a low resolution.

2. Dissecting Microscope

A dissecting microscope is also called stereo microscope. Its  is light illuminated. The image that appears is stereo microscope is  three dimensional. It is used for dissection to get a better look at the larger specimen. You cannot see individual cells because it has a low magnification.

3. Electron microscope

In the early 20th century a significant alternative to the light microscope was developed. First electron microscope develop in 1931. This microscope is Used to see viruses or parts of cells smaller than the limits of resolution of the light microscope. Electron microscope utilizes a beam of electrons instead of visible light and electromagnetic fields in place of optical lenses.

Scanning Electron Microscope (SEM)

SEM use electron illumination. The image is seen in 3-D. It has high magnification and high resolution. The specimen is coated in gold and the electrons bounce off to give you an exterior view of the specimen. The pictures are in black and white.

Transmission Electron Microscope (TEM)

TEM is electron illuminated. This gives a 2-D view. Thin slices of specimen are obtained. The electron beams pass through it. It has high magnification and high resolution

4. Fluorescence Microscopes

An optical microscope that uses fluorescent light to create an image of a sample previously stained with fluorescing dyes called fluorochromes eg.  Rhodamine and Auramine  Used ultra – violet light of very short wavelength which is not visible to the eye. The Dyes transform the invisible short wavelength ultra – violet light in to longer wavelength visible light which make the fluorescent stained organisms, cells, or particles can be seen glowing (fluorescing) against a dark background .Used in molecular biology and immunology research.

5. Confocal Microscopes

Used to create high-resolution images of objects by scanning them with a laser or light beam. There are several types of confocal microscopes, including laser scanning, spinning disk, and programmable array microscopes. Common in biomedical research for 3D imaging of cells and tissues.

6. Phase-Contrast Microscopes

What are the general Applications of Microscopes?

• Medical Diagnostics: Used in pathology and microbiology for detecting diseases.
• Biological Research: Essential for studying cellular structures, bacteria, and viruses.
• Material Science: Helps in analyzing metal structures and nanomaterials.
• Forensic Science: Used for analyzing fibers, hair, and other crime scene evidence.
• Education: Widely used in schools and universities for teaching biology and chemistry.

Anatomy or parts of a compound Microscope

Non optical components of microscope:

• Base: It is U-shaped metallic structure that  supports whole microscope.
• Pillars: It  is  short  upright  path  that  connect  with arm and base.
• Arm: It is a curve metallic handle that  connect with arm by inclination  joint. It supports the stage and body  tube.
• Automatic Stop: It  is  a  small  screw  fitted  at  the  lower of rack and pinion. It is meant  stopping for downward sliding of the body tube.
• Body Tube: It is meant for holding ocular and  objective lenses at its two end.
• Inclination joint: It is used for tilting the microscopy.
• Stage: It is a metallic platform with central  hole fitted to lower part of arm.  Microscopy sides are held on stage.
• Fine Adjustment: Stage moves extremely short distance.  It is required to obtain sharp image.
• Adjustment Screws: There are two pair of screws for  moving the body tube in relation to  the stage
• Draw tube : It is a small tube that remain fixed at  upper and of body tube. It hold eye  piece.
• Rack & Pinions: It is attached with body tube or stage  for begging object under focus.
• Nose piece: A revolving nose piece hold multiple  lenses of different magnification  level.
• Coarse Adjustment: Body tube for stage moves up and  distance. It is meant for briefly objective lens at a proper distance from  object.

Optical Components

Routine use of the microscope

1. Place the microscope on a firm bench so that it does not vibrate.
2. Make sure that it is not be exposed to direct sun light.
3. The user must be seated at the correct height for the convenient use of the microscope.
4. Select the appropriate source of light.
5. Place the specimen on the stage, making sure that the underside of the slide is completely dry.
6. Select the objective to be used. • It is better to begin examination with 10x objective.
7. Adjust the light source until the illumination of image is at its brightest.
8. Adjust the aperture (opening) of the condenser iris according to the specimen being examined.
9. Examine the specimen by systematically moving the slide with the mechanical stage.
10. For a higher magnification, swing the 40x objective into place. Focus the 40x objective, using the fine adjustment.
11. For the highest magnification, add a drop of immersion 80 oil to the specimen and swing the 100x oil immersion objective into place.

Care of Microscope 

• Always carry a microscope using both hands.
• When not in use, a microscope should be protected from dust, moisture, direct sunlight and put in microscope case.
• Keep it standing in place ready for use, but protected by light cover.
• In humid climate it is necessary to cover the microscope in a plastic bag with a drying agent (silica gel) over night to avoid molds growing on the lenses.
• At the end of each day’s work, the surface lenses of the objectives, eyepieces, and condenser should be cleaned using lens tissue.