Microscope Lens Parameters and Their Impact on Microscopic Imaging Quality
Ball difference:
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 light rays with different aperture angles of the original beam cannot intersect at the same position on the main axis, resulting in a diffuse spot (commonly known as a blur circle) at the ideal image plane on the main axis, then the imaging error of this optical system is called spherical aberration.
Huicha:
If a monochromatic conical beam emitted from an object point outside the main axis towards the optical system cannot form a clear point at the ideal image plane after refraction by the optical series, but instead forms a comet shaped spot with a bright tail, the imaging error of this optical system is called coma.
Astigmatism:
The imaging error of an optical system is called astigmatism, which refers to the oblique monochromatic conical beam emitted from an off-axis object point located outside the main axis to the optical system. After being refracted by this optical series, it cannot form a clear image point but can only form a diffuse spot.
Field tune:
The clear image formed by an optical system of a plane object perpendicular to the principal axis, if it is not in an image plane perpendicular to the principal axis, but on a curved surface symmetrical to the principal axis, that is, the optimal image plane is a curved surface, then the imaging error of this optical system is called field curvature. When the focus is on the center of the image, the image around the screen becomes blurry; And when the focus is on the clear image around the frame, the image in the center of the frame begins to blur again.
Color difference:
A beam of white light emitted by a white object into an optical system, after being refracted by the optical system, cannot converge at a single point, forming a colored image spot, which is called chromatic aberration. The reason for color difference is that the same optical glass has different refractive indices for light of different wavelengths, with short wave light having a higher refractive index and long wave light having a lower refractive index.
Distortion:
If the straight line outside the main axis in the plane of the subject becomes a curve after being imaged by an optical system, the imaging error of this optical system is called distortion. Distortion aberration only affects the geometric shape of the image, but does not affect the clarity of the image. This is the fundamental difference between distortion and spherical aberration, coma, astigmatism, and field curvature.
We usually evaluate lens quality 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 a lens to clearly distinguish the fiber details of the subject. The reason that restricts the resolution of a lens is the diffraction phenomenon of light, namely the diffraction spot (Airy spot). The unit of resolution is line pairs per millimeter.
Acuity:
Also known as contrast, it refers to the contrast between the bright and dark parts of an image.
