aberrations中文

Explore the two most prevalent types of distortion, positive and negative, and how they can often be present in very sharp images that are otherwise corrected for spherical, chromatic, comatic, and astigmatic aberrations.

This shows parallel beams from two helium-neon lasers converging to the principal focal point of a 30 cm double convex lens. The rays then enter a diverging lens of focal length -10cm on the right. The laser beams were made visible with a spray can of artificial smoke.

Seidelaberrations

The most important characteristic of a lens is its principal focal length, or its inverse which is called the lens strength or lens "power". Optometrists usually prescribe corrective lenses in terms of the lens power in diopters. The lens power is the inverse of the focal length in meters: the physical unit for lens power is 1/meter which is called diopter.

Learn about comatic aberrations and how they are mainly encountered with off-axis light fluxes and are most severe when the microscope is out of alignment, as well as the result of when these aberrations occur.

Curvature of field in optical microscopy is an aberration that is familiar to most experienced microscopists. This artifact is the natural result of using lenses that have curved surfaces.

Chromatic aberration

An ideal microscope objective produces a symmetrical diffraction limited image of an Airy pattern from an infinitely small object point. The image plane is generally located at a fixed distance from the objective front lens in a medium of defined refractive index. Microscope objectives offered by the leading manufacturers have remarkably low degrees of aberrations and other imperfections, provided the appropriate objective is selected for the task and the objective is utilized properly in accordance with the manufacturer's recommendations. It should be emphasized that objective lenses are not made to be perfect from every standpoint, but are designed to meet certain specifications depending on their intended use, constraints on physical dimensions, and price ranges.

Discover an aberration-free meridional section of a point source of light located at a depth in the specimen layer having a refractive index and imaged with a virtual microscope objective.

Curvature of field in optical microscopy and how it is a common and annoying aberration that is familiar to most experienced microscopists is explained in this featured interactive tutorial.

Explore the relationship between astigmatism and comatic aberrations, and how astigmatism aberrations are manifested by the off-axis image of a specimen point appearing as a line or ellipse instead of a point.

Optical aberration

The principal focal length of a lens is determined by the index of refraction of the glass, the radii of curvature of the surfaces, and the medium in which the lens resides. It can be calculated from the lens-maker's formula for thin lenses.

Aberrationsbg3

Brian O. Flynn, John C. Long, Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

For microscope objectives having apertures, the optical properties and thickness of the medium lying between the front lens element and the specimen affect the calculations necessary to correct for image aberrations.

Spherical aberration

Learn more about chromatic aberrations and how when white light passes through a simple or complex lens system, the component wavelengths are refracted according to their frequency.

Objectives are made with differing degrees of optical correction for both monochromatic (spherical, astigmatism, coma, distortion) and polychromatic aberrations, field size and flatness, transmission wavelengths, freedom from fluorescence, birefringence and other factors contributing to background noise. Depending upon the degree of correction, objectives are generally classified as achromats, fluorites, and apochromats, with a plan designation added to lenses with low curvature of field and distortion. This section addresses some of the more common optical aberrations that are commonly found (and often corrected) in microscope objectives.

For a thin double convex lens, refraction acts to focus all parallel rays to a point referred to as the principal focal point. The distance from the lens to that point is the principal focal length f of the lens. For a double concave lens where the rays are diverged, the principal focal length is the distance at which the back-projected rays would come together and it is given a negative sign. The lens strength in diopters is defined as the inverse of the focal length in meters. For a thick lens made from spherical surfaces, the focal distance will differ for different rays, and this change is called spherical aberration. The focal length for different wavelengths will also differ slightly, and this is called chromatic aberration.

Learn about the most serious of the monochromatic defects that occurs with microscope objectives, the spherical aberration, which causes the specimen image to appear hazy or blurred and slightly out of focus.

Departures in lens action from the ideal conditions of optics are known as aberrations. Optical trains typically suffer from as many as five common aberrations: spherical, chromatic, curvature of field, comatic, and astigmatic.

A demonstration on how internal lens elements in a high numerical aperture dry objective may be correctly adjusted with these varied cover glass thickness and dispersion fluctuations is featured in this tutorial.

Aberrations are divided into two main categories: errors that occur when polychromatic light (white light) is passed through a lens, and errors that are present when only a single wavelength (monochromatic) of light is utilized. The selected references listed in this section contain information about the cause and correction of the most common optical aberrations encountered with microscope and other lens systems. Bear in mind that the optical designer must correct for both polychromatic and monochromatic aberrations simultaneously in the production of well-corrected microscope objectives.