Six Aberrations in Microscopes
Microscope imaging is affected by various aberrations. The main optical component of the microscope is the objective lens, and there are various types of objective lenses, such as achromatic objective lenses, plan objective lenses, etc. Aberration, so as to improve the imaging quality, such as achromatic objective lens is used to eliminate chromatic aberration, plan objective lens is used to eliminate field curvature. The following will introduce the general aberrations of microscopes.
A Chromatic aberration
In the case of polychromatic light as the light source, monochromatic light does not produce chromatic aberration.
White light is composed of seven kinds of red, orange, yellow, green, cyan, blue, and violet. The wavelengths of each light are different, so the refractive index when passing through the lens is also different. In this way, a point on the object side may form a color spot on the image side.
Elimination method: use monochromatic light (add filter), optical design to eliminate
Two Spherical aberration
Spherical aberration is the difference in monochromatic phase of on-axis points due to the spherical surface of the lens. The result of spherical aberration is that after a point is imaged, it is no longer a bright spot, but a bright spot with a bright center and gradually blurred edges. Thus affecting the image quality.
Elimination method: use a combination of convex and concave lenses
Three Coma
Coma is a monochromatic aberration at an off-axis point. When an off-axis object point is imaged with a large-aperture beam, the emitted beam passes through the lens and does not intersect at one point, then the image of a light point will be a comma, which is shaped like a comet, so it is called "coma aberration".
Elimination method: use axial parallel light
Four Astigmatism
Astigmatism is also the off-axis point monochromatic phase difference that affects sharpness. When the field of view is large, the object point on the edge is far away from the optical axis, and the beam tilts greatly, causing astigmatism after passing through the lens. Astigmatism makes the original object point become two short lines separated and perpendicular to each other after imaging, and an elliptical spot is formed after synthesis on the ideal image plane.
Elimination method: through complex lens combination to eliminate.
Five Curvature of field
Image field curvature". When there is field curvature in the lens, the intersection point of the entire beam does not coincide with the ideal image point. Although a clear image point can be obtained at each specific point, the entire image plane is a curved surface. In this way, in the mirror inspection Sometimes the whole face cannot be seen clearly at the same time, which makes it difficult to observe and take pictures.
Objectives for research microscopes are generally plan objectives, which have been corrected for field curvature.
Six Distortion
Except for field curvature, all kinds of phase differences mentioned above affect the sharpness of the image. Distortion is another phase difference in nature, the concentricity of the beam is not destroyed. Therefore, the sharpness of the image is not affected, but the image is distorted in shape compared with the original object.
