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Explanation of Microscope Lens
The lens is the main component of a microscope, and understanding different lenses can help everyone better understand the microscope.
Starting from the aspects of objective lenses, eyepieces, condenser lenses, etc., classify and introduce the different types of lenses.
Objectives
The optical microscope uses an objective lens and an eyepiece for imaging. Observation magnification is the product of the objective lens magnification and the eyepiece magnification. The magnification range of a regular optical microscope is 10 × To 1000 ×， And some optical microscopes have a magnification of up to 2000 ×。
The objective lens consists of multiple lenses, used to magnify objects and project larger images. Depending on the focal length, lenses with different magnifications can be installed, such as 4 ×、 ten ×、 forty × And 50 ×。 In addition to magnification, the performance indicators of the objective lens also include numerical aperture and working distance.
The light transmitted through the lens will produce chromatic aberration (oozing), and its refractive index varies depending on the wavelength. In order to prevent color difference, the following lenses have been developed:
Achromatic lens: This type of lens is used to keep the refractive index of two wavelengths (colors) of light consistent. This type of lens is widely used, partly due to its reasonable price.
Semi apochromatic lens: This type of lens is used to maintain consistency in the refractive indices of three wavelengths (colors) of light. This type of lens has the transmittance required to observe ultraviolet light with a wavelength of approximately 340 nm, making it suitable for fluorescence observation.
Apochromatic lens: Like a semi apochromatic lens, this type of lens is used to maintain the refractive index of three wavelengths (colors) of light consistent. This type of lens has a large numerical aperture and good resolution, so it is usually used in scientific research fields that require detailed observation. This type of lens has high performance, therefore its price is also higher.
Plan lens: The field distortion of this type of lens is corrected, so the center and periphery of the lens are focused. If the field aberration of the three types of lenses mentioned above is corrected, they can be called flat field achromatic lenses, flat field fluorite lenses, and flat field apochromatic lenses, respectively. In most cases, it is marked with "PLAN" on the side of the lens.
Immersion lens: This type of lens can increase the numerical aperture by filling liquid between the objective lens and the specimen, thereby achieving higher resolution. Immersion lenses that work with oil are called oil immersion lenses, while immersion lenses that work with water are called water immersion lenses. The side of the oil immersed lens is marked with "HI" or "OIL", while the side of the water immersed lens is marked with "W" or "WATER".
Eyepiece
An eyepiece is a lens installed on the observer's side. After the image is magnified by the objective lens, it is further magnified by the eyepiece to facilitate observation. The eyepiece consists of 1 to 3 lenses, and a field of view aperture can also be set to eliminate unnecessary reflected light and aberration.
Depending on the magnification (e.g. 7 × And 15 ×）， Different types of eyepieces can be used. In addition to magnification, lens performance can also be expressed as the number of fields of view, which is the range of the field of view.
Contrary to objective lenses, the higher the magnification of the eyepiece, the shorter its length.
Depending on the structure or application of the field of view diaphragm, the following lenses can be installed:
Huygens lens: The Huygens lens consists of two flat convex lenses. This type of lens is used for low magnification observation, characterized by the field of view diaphragm located in the lens barrel.
Ramsden lens: The characteristic of this type of lens is that the field of view aperture is not in the lens barrel.
Periplan lens: Even around the field of view, this type of lens can correct for chromatic aberration in magnification and other characteristics, achieving clean observation.
Compensation eyepiece: An eyepiece specifically designed for use with apochromatic lenses. Due to the fact that the blue image generated by the apochromatic objective is larger than the red image, which means there is residual lateral chromatic aberration, while the compensating eyepiece is designed with a red image larger than the blue image to offset the lateral chromatic aberration of the apochromatic objective. The image field curvature of compensating eyepieces is quite severe, and due to the development of new flat image eyepieces, compensating eyepieces are now rarely used.
Wide field of view lens: This type of lens can achieve a wide field of view, mainly used for observing organisms and minerals.
Condenser
A spotlight is a lens installed below the stage. A spotlight can adjust the amount of light to evenly illuminate an object. This type of lens is suitable for high magnification observation. Spotlight lenses can be divided into various types, including ordinary "Abbe spotlights" and "achromatic spotlights" for correcting color differences.
Abbe condenser: designed by Ernst Abbe, a master at the German University of Optics (one of the founders of Zeiss). The Abbe condenser consists of two lenses and has good focusing ability. However, when the numerical aperture of the objective lens is higher than 0.60, chromatic and spherical aberration will be displayed. Therefore, it is often used on ordinary microscopes.
Achromatic and spherical aberration condenser: This type of condenser is also known as "achromatic and spherical aberration condenser" and "Qiming condenser". It is composed of a series of lenses, which have a high degree of correction for chromatic aberration and spherical aberration, and can obtain ideal images. It is the highest quality condenser in bright field microscopy, with an NA value of 1.4.
About Magnification
The total observation magnification is expressed as the product of the objective magnification and the eyepiece magnification. For example, if the magnification of the objective lens is 20 ×， The magnification of the eyepiece is 10 ×， Then the total magnification is 200 ×。
one × Refers to the observer observing the state of an object at a distance of 250 mm. 250 mm is considered the easiest distance to be observed by the human eye. This distance is called the apparent distance.
The magnification of an eyepiece is equal to the apparent distance divided by the focal length of the lens.
How to clean the lens
After using the microscope, it is necessary to clean dust, oil, and dirt, as the lens can easily adhere to dust, fingerprints, or culture medium during use.
When cleaning the lens, the following tools are mainly needed:
Air blowing
Lens cleaning paper
Cotton swab
Cleaning agents (manufacturer recommended cleaning agents, anhydrous alcohol, mixtures of ether and alcohol, distilled water, etc.)
