Views: 54
The Optical(Light) Microscope
The light microscope, also known as the optical microscope, is one of the most widely used types of microscopes. It uses visible light and a series of lenses to magnify and resolve the details of a specimen. The light microscope has been instrumental in many scientific fields, including biology, medicine, materials science, and more.
Depending on their strength,these two lenses can routinely provide a magnification of over X400.
The light microscope have had profound influence in microbiology and cell biology but its however have a limit in the amount of details it can show. This limit is set by its resolving power. The resolving power is the minimum distance by which two points must be separate for them to be perceived as two separate points rather than a single fused point .For light microscope these image should be 2 μm apart .The limited resolution of light microscope is imposed by the wavelength of the visible light and it means that more can be gained by magnifying the object more than 1500 times .
These puts a limit in the amount of structural details that can be detected within the cell . Higher magnification can be achieved by using a special objective lens with a fluid situated between the lens (oil emersion ) but even then it is not possible to achieve magnification of 2000
Types of Light Microscopes
- 1. Monocular microscopes
Monocular microscopes are those microscopes having one eye piece lens fixed to the microscope. They include
a) The standard Microscope
These are the ordinary common light microscope. Its stage is not permanently fixed and it can be inclined and is movable
- The standard Microscope
- Fixed Inclined Limb Microscope
The stage is maintained in a horizontal plane and the body tube is inclined towards the user , in some models , the rotation of the body tube in a horizontal plane is possible . These may be useful in teaching as the teacher can share the instrument with students without moving or exchanging places with students
- Inverted Microscopes
These type of microscope have its source of light on the upper side and the specimen on the slide is placed on the stage and a serrated wheel is turned to move the single objective lens up and down so as to achieve focus .
Different degrees of magnification are achieved by inserting one , two or three magnifying tubes between the objective and the eyepiece
Inverted microscopes operate at lower magnification than the other microscopes e.g. X 60- X200. They are therefore suitable for junior work
- Binocular microscopes
Monocular microscopes leads to eyes straining, these can be reduced by using binocular microscopes which have two eyepiece lens mounted to microscope . They can have either single or double objective lens
STRUCTURAL COMPONENTS OF MICROSCOPES
The three basic, structural components of a compound microscope are the head, base and arm.
- Head/Bodyhouses the optical parts in the upper part of the microscope
- Base of the microscope supports the microscope and houses the illuminator
- Arm connects to the base and supports the microscope head. It is also used to carry the microscope.
Structurally, a microscope consists of two main components: the optical parts and the mechanical parts.
-
Optical Parts:
Optical parts comprises of all components that are directly related with the transmission of light through the microscope . It consists of the objective lens, eyepiece lens , condensor and the mirror.
2. Mechanical Parts:
The mechanical parts consist of all components that are involved in forming the framework and those used in adjustment process of the microscope . this includes; the stage, the clips , the arm, the base, the body tube, the coarse and fine adjustment knobs
Parts and Functions of Optical Microscope 
Eyepiece or Ocular is what you look through at the top of the microscope. Typically, standard eyepieces have a magnifying power of 10 xs. Optional eyepieces of varying powers are available, typically from 5x-30x.
Eyepiece Tube holds the eyepieces in place above the objective lens. Binocular microscope heads typically incorporate a diopter adjustment ring that allows for the possible inconsistencies of our eyesight in one or both eyes. The monocular (single eye usage) microscope does not need a diopter. Binocular microscopes also swivel (Interpupillary Adjustment) to allow for different distances between the eyes of different individuals.
Objective Lenses are the primary optical lenses on a microscope. They range from 4x-100x and typically, include, three, four or five on lens on most microscopes. Objectives can be forward or rear-facing.
Nosepiece houses the objectives. The objectives are exposed and are mounted on a rotating turret so that different objectives can be conveniently selected. Standard objectives include 4x, 10x, 40x and 100x although different power objectives are available.
Coarse and Fine Focus knobs are used to focus the microscope. Increasingly, they are coaxial knobs – that is to say they are built on the same axis with the fine focus knob on the outside. Coaxial focus knobs are more convenient since the viewer does not have to grope for a different knob.
Stage is where the specimen to be viewed is placed. A mechanical stage is used when working at higher magnifications where delicate movements of the specimen slide are required.
Stage Clips are used when there is no mechanical stage. The viewer is required to move the slide manually to view different sections of the specimen.
Aperture is the hole in the stage through which the base (transmitted) light reaches the stage.
Illuminator is the light source for a microscope, typically located in the base of the microscope. Most light microscopes use low voltage, halogen bulbs with continuous variable lighting control located within the base.
Condenser is used to collect and focus the light from the illuminator on to the specimen. It is located under the stage often in conjunction with an iris diaphragm.
Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser and below the stage. Most high quality microscopes include an Abbe condenser with an iris diaphragm. Combined, they control both the focus and quantity of light applied to the specimen.
Condenser Focus Knob moves the condenser up or down to control the lighting focus on the specimen.