Microscope Parts & Specifications Labeled Diagram - what is the function of objective lenses in microscope

 2024-08-09 10:02:58

In the optical design of microscope objectives, commonly the larger is an N.A. and the higher is a magnification, the more difficult to correct the axial chromatic aberration of a secondary spectrum. In addition to axis chromatic aberration, various aberrations and sine condition must be sufficiently corrected and therefore the correction of the secondary spectrum is far more difficult to be implemented. As the result, a higher-magnification apochromatic objective requires more pieces of lenses for aberration correction. Some objectives consist of more than 15 pieces of lenses. To correct the secondary spectrum satisfactorily, it is effective to use "anomalous dispersion glass" with less chromatic dispersion up to the secondary spectrum for the powerful convex lens among constituting lenses. The typical material of this anomalous dispersion glass is fluorite (CaF2) and has been adopted for apochromatic objectives since a long time ago, irrespective of imperfection in workability. Recently, optical glass with a property very close to the anomalous dispersion of fluorite has been developed and is being used as the mainstream in place of fluorite.

Asphericlenses advantages disadvantages

The purposes of optical microscopes are broadly classified into two; "biological-use" and "industrial-use". Using this classification method, objective lenses are classified into "biological-use" objectives and "industrial-use" objectives. A common specimen in a biological use is fixed in place on the slide glass, sealing it with the cover glass from top. Since a biological-use objective lens is used for observation through this cover glass, optical design is performed in consideration of the cover glass thickness (commonly 0.17mm). Meanwhile, in an industrial use a specimen such as a metallography specimen, semiconductor wafer, and an electronic component is usually observed with nothing covered on it. An industrial-use objective lens is optically designed so as to be optimal for observation without any cover glass between the lens end and a specimen.

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Aspherical lens photography

Aspherical lenses, by their design, help to mitigate spherical aberration, leading to improved focusing of light rays and producing images with better clarity and sharpness.

Photography or image pickup with a video camera has been common in microscopy and thus a clear, sharp image over the entire field of view is increasingly required. Consequently, Plan objective lenses corrected satisfactorily for field curvature aberration are being used as the mainstream. To correct for field curvature aberration, optical design is performed so that Petzval sum becomes 0. However, this aberration correction is more difficult especially for higher-magnification objectives. (This correction is difficult to be compatible with other aberration corrections) An objective lens in which such correction is made features in general powerful concave optical components in the front-end lens group and powerful concave ones in the back-end group.

Objective lenses are roughly classified basically according to the intended purpose, microscopy method, magnification, and performance (aberration correction). Classification according to the concept of aberration correction among those items is a characteristic way of classification of microscope objectives.

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Define asphericeye

An objective lens is the most important optical unit that determines the basic performance/function of an optical microscope To provide an optical performance/function optimal for various needs and applications (i.e. the most important performance/function for an optical microscope), a wide variety of objective lenses are available according to the purpose.

An optical microscope is used with multiple objectives attached to a part called revolving nosepiece. Commonly, multiple combined objectives with a different magnification are attached to this revolving nosepiece so as to smoothly change magnification from low to high only by revolving the nosepiece. Consequently, a common combination lineup is comprised from among objectives of low magnification (5x, 10x), intermediate magnification (20x, 50x), and high magnification (100x). To obtain a high resolving power particularly at high magnification among these objectives, an immersion objective for observation with a dedicated liquid with a high refractive index such as immersion oil or water charged between the lens end and a specimen is available. Ultra low magnification (1.25x, 2.5x) and ultra high magnification (150x) objectives are also available for the special use.

Asphericlens meaning

On the other hand, aspherical lenses have varying curvatures across their surfaces, deviating from the traditional spherical shape. This enables them to counteract a wider range of optical aberrations, producing sharper and more accurate images.

In conclusion, aspherical camera lenses, with their non-spherical surface design, represent a vital breakthrough in modern photography. By effectively correcting optical aberrations and producing higher image quality, they have become indispensable tools for photographers across various genres. Their ability to deliver sharp, distortion-free images, especially in wide-angle scenarios, makes them a preferred choice for many photography enthusiasts and professionals alike. Despite their higher cost and potential lens flare concerns, the advantages they offer far outweigh the drawbacks, making aspherical lenses an essential asset in the pursuit of capturing stunning and breathtaking images.

Microscopes use convex lenses in order to focus light. Image from http://clubsciencekrl.blogspot.com/. Microscope objectives contain lenses but are not as ...

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Define asphericlenses

The main difference between spherical and aspherical lenses lies in their curvature. Spherical lenses have a constant curvature across the entire lens surface, resembling a perfect sphere. This results in limitations in correcting various optical aberrations, which can lead to decreased image quality, especially towards the edges of the frame.

Asphericpronunciation

In the realm of photography, the aspherical camera lens, commonly abbreviated as ASPH lens, represents a significant technological advancement. Unlike traditional spherical lenses, which have a smooth, curved surface, aspherical lenses incorporate non-spherical elements that deviate from the standard spherical shape. These non-spherical elements allow the lens to better focus light, reducing various optical aberrations that can affect image quality.

AsphericIOL

Meanwhile, an objective lens for which the degree of chromatic aberration correction to the secondary spectrum (g ray) is set to medium between Achromat and Apochromat is known as Semiapochromat (or Flulorite).

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Spherical aberration is a common optical phenomenon that occurs in lenses with a uniform curvature, such as spherical lenses. It causes light rays passing through the edges of the lens to converge at a different focal point than those passing through the center. As a result, the image may appear blurred or lack sharpness.

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Axial chromatic aberration correction is divided into three levels of achromat, semiapochromat (fluorite), and apochromat according to the degree of correction. The objective lineup is divided into the popular class to high class with a gradual difference in price. An objective lens for which axial chromatic aberration correction for two colors of C ray (red: 656,3nm) and F ray (blue: 486.1nm) has been made is known as Achromat or achromatic objective. In the case of Achromat, a ray except for the above two colors (generally violet g-ray: 435.8nm) comes into focus on a plane away from the focal plane. This g ray is called a secondary spectrum. An objective lens for which chromatic aberration up to this secondary spectrum has satisfactorily been corrected is known as Apochromat or apochromatic objective. In other words, Apochromat is an objective for which the axial chromatic aberration of three colors (C, F, and g rays) has been corrected. The following figure shows the difference in chromatic aberration correction between Achromat and Apochromat by using the wavefront aberration. This figure proves that Apochromat is corrected for chromatic aberration in wider wavelength range than Achromat is.

A variety of microscopy methods have been developed for optical microscopes according to intended purposes. The dedicated objective lenses to each microscopy method have been developed and are classified according to such a method. For example, "reflected darkfield objective (a circular-zone light path is applied to the periphery of an inner lens)", "Differential Interference Contrast (DIC) objective (the combination of optical properties with a DIC( Nomarski）prism is optimized by reducing lens distortions)", "fluorescence objective (the transmittance in the near-ultraviolet region is improved)", "polarization objective (lens distortions are drastically reduced)", and "phase difference objective (a phase plate is built in) are available.

Aspherical lenses are designed with complex surfaces, characterized by a combination of convex and concave curvature. This intricate shaping of the lens surface helps in gathering and transmitting light rays more efficiently, ultimately leading to improved image sharpness and reduced distortions.