Principles of Imaging (Geometric Imaging) of Microscopy
15 Jul 2022
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The reason why the microscope can magnify the inspected object is achieved through the lens. Single-lens imaging has aberrations, which seriously affect the imaging quality. Therefore, the main optical components of the microscope are composed of lenses. From the performance of the lens, only the convex lens can magnify, but the concave lens cannot. Although the objective lens and eyepiece of the microscope are composed of lenses, they are equivalent to a convex lens. In order to facilitate the understanding of the magnification principle of the microscope, briefly explain the five imaging laws of the convex lens:
(1) When the object is located beyond the double focal length of the object side of the lens, a reduced inverted real image is formed within the double focal length of the image side and outside the focus;
(2) When the object is located at twice the focal length of the object side of the lens, an inverted real image of the same size is formed on the double focal length of the image side;
(3) When the object is located within the double focal length of the object side of the lens, but outside the focus, an enlarged inverted real image is formed outside the double focal length of the image side;
(4) When the object is located at the focal point of the object side of the lens, the image side cannot be imaged;
(5) When the object is located within the focal point of the object side of the lens, there is no image formation on the image side, and an enlarged upright virtual image is formed on the same side of the lens object side farther than the object.
The imaging principle of the microscope is to use the rules of (3) and (5) above to enlarge the object. When the object is between F-2F in front of the objective lens (F is the focal length of the object side), a magnified inverted real image will be formed beyond the double focal length of the image side of the objective lens. In the design of the microscope, this image falls within one focal length F1 of the eyepiece, so that the first image (intermediate image) magnified by the objective lens is magnified again by the eyepiece, and finally it is on the object side of the eyepiece (intermediate image). At the same side of the human eye), an enlarged upright (relative to the intermediate image) virtual image is formed at the photopic distance (250mm) of the human eye. Therefore, when we inspect the microscope, the image seen through the eyepiece (without additional conversion prism) is in the opposite direction to the image of the original object.
(1) When the object is located beyond the double focal length of the object side of the lens, a reduced inverted real image is formed within the double focal length of the image side and outside the focus;
(2) When the object is located at twice the focal length of the object side of the lens, an inverted real image of the same size is formed on the double focal length of the image side;
(3) When the object is located within the double focal length of the object side of the lens, but outside the focus, an enlarged inverted real image is formed outside the double focal length of the image side;
(4) When the object is located at the focal point of the object side of the lens, the image side cannot be imaged;
(5) When the object is located within the focal point of the object side of the lens, there is no image formation on the image side, and an enlarged upright virtual image is formed on the same side of the lens object side farther than the object.
The imaging principle of the microscope is to use the rules of (3) and (5) above to enlarge the object. When the object is between F-2F in front of the objective lens (F is the focal length of the object side), a magnified inverted real image will be formed beyond the double focal length of the image side of the objective lens. In the design of the microscope, this image falls within one focal length F1 of the eyepiece, so that the first image (intermediate image) magnified by the objective lens is magnified again by the eyepiece, and finally it is on the object side of the eyepiece (intermediate image). At the same side of the human eye), an enlarged upright (relative to the intermediate image) virtual image is formed at the photopic distance (250mm) of the human eye. Therefore, when we inspect the microscope, the image seen through the eyepiece (without additional conversion prism) is in the opposite direction to the image of the original object.