MICROSCOPES Faculty of Applied Medical Sciences Walaa Mal Histopathology Teaching Assistant

Contents Introduction Definitions Types of microscopes - Compound light microscopes - Electron microscopes Care of microscopes

Introduction Microscopes: “Micro” refers to tiny, “scope” refers to view or look at.

Introduction Microscopes range from a simple magnifying glass to the expensive electron microscope. The compound light microscope (CLM) is the most common instrument used in education today.

Introduction Its an instrument containing one or two lenses, which magnifies, and a variety of knobs to resolve (focus) the picture. It is a rather simple piece of equipment to understand and use.

Definitions Microscopes: are tools used to enlarge images of small objects so as they can be studied. Magnification: the increase in an object’s apparent size. Resolution: the power of microscope to clearly show detail.

Magnification Resolution

Types of microscopes 1- Compound Light Microscopes 2- Electron Microscopes - Transmission Electron Microscopes - Scanning Electron Microscopes

Compound Light Microscope

Compound Light Microscopes (LM) With this type of microscope the specimen (thin sliced enough to be transparent or sometimes stained) is mounted on a glass slide to be viewed. The slide is placed on the stage and a light source (a light bulb or mirror in the base) directs the light upwards.

Compound Light Microscopes (LM) Light passes through the specimen and through the objective lens, which is positioned directly above the specimen. The objective lens: a set of objective lenses is located on the rotating nosepiece enlarges the image of the specimen with different powers of magnification.

Compound Light Microscopes (LM) Objective lenses: a- the lowest power lens is 3.5 or 4x, and is used primarily for initially finding specimens. b- the most frequently used objective lens is the 10x lens, which gives a final magnification of 100x with a 10x ocular lens. c- typical high magnification lenses are 40x and 97x or 100x. The later two magnifications are used exclusively with oil in order to improve resolution.

Compound Light Microscopes (LM) From the objective lens, the magnified image is projected up through the body tube to the ocular lens in the eyepiece where it is magnified further (10x). To compute the total magnification of a microscope, multiply the power of magnification of the lens being used (40x, 100x) by the power of magnification of the ocular or eyepiece lens (10x) example: 40 X 10= 400X total power magnification. The resolution power of LM’s is limited by the physical characteristics of light (at powers of magnification beyond about 2000X, the image of the specimen becomes blurry.)

Compound Light Microscopes (LM) Note : Other than the compound microscope, a simpler instrument for low magnification use may also be found in the laboratory. This is the stereo microscope, or dissecting microscope. Stereo microscopes usually have a binocular eyepiece tube, a long working distance, and a range of magnifications, but there is no improvement in resolution. Such, “false magnification” is rarely worth the expense.

Stereo or Dissecting Microscope

Electron Microscopes Used to view extremely small objects. Beam of electrons, rather than light, produces an enlarged image. Electron microscopes are more powerful than LM’s. There are several types of EM’s.

Transmission Electron Microscopes Can magnify objects up to 200,000 times. Projects image on to a screen or photographic plate. Used to produce greatly magnified images of internal details of a specimen. Can not be used to view living specimens.

Transmission Electron Microscopes

Scanning Electron Microscopes Produces a 3 dimensional image. Specimens are not sliced but are sprayed with a fine metal coating. A beam of electrons is passed over the surface of the metal coating to emit a shower of electrons. Showered electrons are projected onto a fluorescent screen or photographic plate. SEM’s produce greatly magnified image of surface details of specimens. Can magnify up to 100,000 times. Can not be used to view living specimens.

Scanning Electron Microscopes

Care of Microscopes Everything on a good quality microscope is unbelievably expensive, so be careful. Hold a microscope firmly by the stand, only. Never grab it by the eyepiece holder, for example. Hold the plug (not the cable) when unplugging the illuminator. Since bulbs are expensive, and have a limited life, turn the illuminator off when you are done.

Care of Microscopes A lways make sure the stage and lenses are clean before putting a way the microscope. Never use anything but good quality lens tissue on any optical surface, with appropriate lens cleaner or distilled water; organic solvents may separate damage the lens elements or coatings. Cover the instrument with the dust jacket when not in use. Focus smoothly; don’t try to speed the focusing process or force anything.