refractive index of the solid immersion lens n3 refractive index As a second benchmark a high numeric aperture oil objective is chosen which GetPDFServlet?filetype=pdf&id=JAPIAU&idtype= cvips&prog. reconfigured as a variable numerical aperture microscope condenser by depositing a inner edge of the top aperture of the metal cage of the oil- immersion objective lens Sorry, there is no online preview for this file type. Diffraction: “light waves change direction when passing through an opening or some microscope objectives use oil (n = for immersion oil) to increase the n Numerical Aperture is a way to define the cone angle of light which passes .

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The refractive index of the imaging medium is critical in determining the working numerical aperture of a microscope objective.

Immersion Oil and Refractive Index | MicroscopyU

A dramatic increase in numerical aperture is observed when the objective is designed to operate with an immersion medium imjersion as oil, glycerin, or water between the front lens and the specimen cover glass. This tutorial explores how changes in the refractive index of the imaging medium can affect how light rays are captured by the objective, which has an arbitrarily fixed angular aperture of 65 degrees.


The 12 hypothetical light rays emanating from the specimen pass through the cover glass, but ikmersion four are refracted into the objective at the lowest refractive index n value.

The other eight light rays are either stopped by the objective front lens housing, refracted into the air surrounding the objective, or reflected back into the cover glass.

Oil immersion

These light rays and do not contribute to formation of the image. As the refractive index value of the imaging medium is increased by moving the slider to the right, successively more light rays are able to refract into the objective front lens until, at the highest n value, all 12 rays enter the objective.

One of the most important factors in determining the resolution of an objective is the angular immdrsion, which has a practical upper limit of about 72 degrees with a sine value of 0. When combined with refractive index, the product: Numerical aperture is generally the most important design criteria other than magnification to consider when selecting a microscope objective.

Values range from 0. As numerical aperture values increase for a kil of objectives of the same magnification, we generally observe a greater light-gathering ability and increase in resolution. Objective numerical aperture can be dramatically increased by designing the objective to be used with an immersion medium, such as oil, glycerin, or water.


By using immesrion immersion medium with a refractive index similar to that of the glass coverslip, image degradation due to thickness variations of the cover glass are practically eliminated whereby rays of wide obliquity lbjective longer undergo refraction and are more readily grasped by the objective.

Typical immersion oils have a refractive index of 1. Light rays passing through the specimen encounter a homogeneous medium between the coverslip and immersion oil and are not refracted as they enter the lens, but only as they leave its upper surface.

It follows that if the specimen is placed at the aplanatic point of the first objective lens, imaging by this portion of the lens system is totally free of spherical aberration. Matthew Parry-Hill and Michael W. Back to Introduction to Microscope Objectives.

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