SOP – Malaria Microscopy - NVBDCP

Quality Assurance of Malaria Diagnostic tests7.1.5.2.2 ObjectivesThe objectives are screwed on to the rotating nosepiece which is attached to the lower endof the tube. They are usually 3-4 in number and designated according to their focal lengths.• low power dry objective : 16 mm• high Power dry objective: 4 mm• oil Immersion objective : 1.6 mmTheir magnifying power and/or their numerical aperture may also be engraved on them. Theeyepieces or the oculars are usually designated by their magnification eg. 10x.7.1.5.2.2.1 Oil-immersion objectiveThis is the most frequently used objective because of the greater magnification andresolution which is required to study the morphology of parasites like malaria parasites.Some of the monocular and all the binocular compound microscopes, have 100x oilimmersion lenses. These can be identified by a red band around the lens housing. Atmagnifications greater than about 500x, light is refracted too much, as it passes through airto yield good resolving power. Thus, optics for these higher magnifications are made to usewith a high grade mineral oil as the medium for transmitting light. It is imperative that onlyimmersion oil is used and the lens is cleaned thoroughly with lens paper after each useeveryday.7.1.5.2.3 Body tubeThis contains mirrors and prisms which direct the image to the ocular lens/es.7.1.5.2.4 NosepieceThis holds the objective lenses and rotates with a positive click for each lens.7.1.5.3 Illuminating partsThis consists of a condenser, an iris diaphragm, a mirror and the light source situated belowthe stage.7.1.5.3.1 CondenserThe condenser is made up of a system of convex lenses. It concentrates the light raysreflected by the mirror to the object plane in the optical axis. The condenser can be raised orlowered. Lowering of the condenser diminishes illumination, whereas, raising it increases theillumination. While using oil-immersion objective, the condenser is completely raised as itrequires more light. When the other objectives are used, it is lowered suitably. Thecondensers moveup and down to focus the light beam.7.1.5.3.2 Iris diaphragmThis helps to regulate the amount of light. It is opened widely when the oil immersionobjective is used, as it requires maximum light and closed partially when the other objectivesare in use. The diaphragm is located just below the stage and controls the amount of lightwhich passes to the specimen and can drastically affect the focus of the image.SOP – Malaria Microscopy© Copyright to Dte. NVBDCP Only. Any modification are prohibited