Microscope Objective Lens

More on Microscope Objective Lens

admin — Wed, 04 Jul 2007 15:03:06 +0000

Lensmaker’s Equation

The focal length of a lens in air can be calculated from the lensmaker’s equation.

Let

f is the focal length of the lens,
n is the refractive index of the lens material,
R1 is the radius of curvature of the lens surface closest to the light source,
R2 is the radius of curvature of the lens surface farthest from the light source, and
d is the thickness of the lens or the distance along the lens axis between the two surface vertices.

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Microscope Objective Lens: Chromatic Aberration

admin — Wed, 04 Jul 2007 14:33:33 +0000

Chromatic aberration is caused by the scattering of the microscope objective lens material. Chromatic aberration of a microscope objective lens is seen as fringes of color around the image. It can be lessened by using an achromatic doublet or achromat, in which two materials with different dispersions are bonded together to form a single lens. Such would reduce the amount of chromatic aberration over a certain range of wavelengths. However, it does not produce perfect correction. The use of achromats was an important step development of the optical microscope.

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Microscope Objective Lens: Coma

admin — Wed, 04 Jul 2007 14:32:38 +0000

Another type of aberration is coma. The term derives its name from the comet-like appearance of the deviated image. Coma occurs when an object off the optical axis of the microscope objective lens is reflected. Rays pass through the lens at an angle to the axis ?.

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Microscope Objective Lens: Spherical Aberration

admin — Wed, 04 Jul 2007 14:32:01 +0000

Spherical aberration happens because spherical surfaces are not the ideally shaped. Spheres are the simplest shape to which glass can be ground and polished. Spherical aberration causes light beams to become parallel to each other but at the same time causes them to move away from the lens axis. Moving the light beams away causes them to be focused in a slightly different place than beams close to the axis. This manifests as a blurring of the image.

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Microscope Objective Lens

admin — Wed, 04 Jul 2007 14:30:31 +0000

Lens construction

Microscope objective lens may be spherical. Such lens surfaces have spherical curvature. The front and back surfaces of the microscope objective lens can each be imagined to be part of the surface of a sphere.

Each surface can be:
1. convex or bulging outwards from the lens
2. concave or depressed into the lens
3. planar or flat

The line joining the centers of the spheres that make up the lens surfaces is called the axis of the lens. In almost all cases, the lens axis passes through the physical center of the microscope objective lens.

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