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Leica objektiv4/9/2023 ![]() Remove excess oil using a lens cleaning tissue with a single sweep across the lens. Immersion oil can (and will) penetrate and damage microscope components and objectives not suited for immersion. Even if you plan to examine other slides, you should remove the oil from the objective at this stage to prevent possible contamination of other parts of the microscope.Although high-power objectives have a spring-loaded nose, coarse focusing at this stage can easily result in cracking the cover glass or slide and can also damage the objective front lens. ![]() Use only the fine focus to adjust the field of view. You can then look down the eyepieces again.Some oil objectives have a concave front lens which means you should also add a drop of oil to the objective to prevent air bubbles becoming trapped in the concave lens. Swing the high-power objective into place and (continuing to look at the stage from the side), use the coarse and then the fine focus to bring the objective front lens into contact with the oil. Whilst looking from the side of the microscope, carefully place one drop of immersion oil directly onto the glass coverslip.Swing the nosepiece (the turret which houses the objectives) around between the 40x and 100x objective, but do not fully engage the high-power objective.Work up to the 40x objective and set up the microscope for Koehler illumination. ![]() Start by viewing your sample with a low-magnification objective to find the area of interest on your slide.The purpose of the immersion liquid is to decrease the amount of refraction and reflection of light from the specimen and increase the ability of the objective to capture this otherwise deviated light (refer to Figure 1). Any light rays which are refracted into the air, reflected by the glass coverslip, or actually blocked by the metal housing of the objective front lens do not contribute to the image formation. ![]() When light passes from one medium to another (for example, through glass to air) it refracts - in other words, it bends and scatters. Having an immersion liquid in place of the air gap between the front lens of an objective and the cover glass or glass coverslip of a specimen increases the resolution of an objective. Resolution and NA will be covered in other articles, but we will now examine immersion techniques available to microscopists which allow the imaging of specimens at high magnification while overcoming some of the limits of resolution. In brief, the NA of an objective is the ability to gather light from a specimen whereas resolution is the ability of an objective to distinguish details in the specimen. One of the main problems in light microscopy is to overcome some of the limits of optical resolution and to increase the numerical aperture (NA) of the system. ![]()
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