Microscope lens parameters and their impact on the quality of microscopic imaging
Aberration is an important aspect that affects image quality, and there are six common types of aberrations:
Ball deviation:
A monochromatic conical beam emitted from a certain point on the main axis towards the optical system. After being refracted by the optical series, if the original beam of light with different aperture angles cannot intersect at the same position on the main axis, or even form a diffuse light spot (commonly known as a blur circle) at the ideal image plane on the main axis, the imaging error of this optical system is called spherical aberration.
Wisdom difference:
If a monochromatic conical beam of light emitted from a point outside the main axis towards the optical system is refracted by the optical series and cannot form a clear point on the ideal image plane, but instead forms a comet shaped spot with a bright tail, the imaging error of this optical system is called coma.
Astigmatism:
The oblique monochromatic conical beam emitted by a point located outside the main axis towards the optical system cannot form a clear image point after being refracted by the optical series, but can only form a diffuse spot. The imaging error of this optical system is called astigmatism.
Field music:
The clear image formed by an optical system of a plane object perpendicular to the main axis, if it is not in a plane perpendicular to the main axis, but on a curved surface symmetrical about the main axis, i.e., the preferred image surface is a curved surface, then the imaging error of this optical system is called field curvature. When the image at the center of the screen is clear, the image around the screen is blurry; When the image around the screen is focused until it is clear, the image in the center of the screen begins to blur again.
Color difference:
A beam of white light is emitted from a white object into the optical system, and after being refracted by the optical system, the colored light cannot converge at a single point, forming a colored image spot called chromatic aberration. The reason for color difference is that the same optical glass has different refractive indices for different wavelengths of light, with higher refractive indices for short wave light and lower refractive indices for long wave light.
Distortion:
The imaging error of an optical system is called distortion when a straight line outside the main axis of the subject plane becomes a curve after being imaged by the optical system. Aberration only affects the geometric shape of the image and does not affect its clarity. This is the fundamental difference between distortion and spherical aberration, coma, astigmatism, and field curvature.
When evaluating lens quality, we usually judge it based on several practical parameters such as resolution, sharpness, and depth of field.
Resolution:
Also known as discrimination rate or resolution, it refers to the ability of the lens to clearly distinguish the fiber details of the subject matter. The reason for restricting the lens resolution is the diffraction phenomenon of light, namely diffraction spot (Airy spot). The unit of resolution is line pairs per millimeter.
