3. Microscope simple, compound & stereo - Basics

3. Microscope simple, compound & stereo - Basics

• 1.
  MICROSCOPY 1 SIMPLE MICROSCOPE Asimple 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 microscopyclassified 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. DARKFIELDMICROSCOPES  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.