Because of the objective condition, no optical system can produce the ideal image, and the existence of various difference influences the image quality. The following is a brief description of the differences.
1. Color difference
Chromatic aberration is a serious defect of lens imaging, which occurs in the case of polychromatic light, the single color does not produce chromatic aberration. White light by the red Orange Green cyan violet seven kinds of composition, the wavelength of a variety of lights are different, so the refractive index through the lens is also different, so that the object of a point, in the square may form a stain.
Chromatic aberration generally has the position chromatic aberration, the magnification rate chromatic aberration. The position color errand looks like in any position to observe, has the color spot or the Halo ring, causes the like to be vague. The magnification color errand is like a colored edge.
2. Ball Difference
The spherical aberration is the monochromatic difference between the points on the axis and is caused by the spherical surface of the lens. The result of the ball difference is that after a point imaging, it is not a bright spot, but a bright spot with a bright and blurred edge. Thus affecting imaging quality.
The correction of the spherical aberration often uses the lens combination to eliminate, because the convex, the concave ball difference is opposite, may choose the different material the convex and concave lens agglutination to give eliminates. In the old model microscope, the spherical aberration of the objective lens is not completely corrected and should be matched with the corresponding compensating eyepiece to achieve the correct effect. The spherical aberration of the general new microscope is completely eliminated by the objective lens.
1, Hui Difference
The difference is the monochromatic difference of the axial point. When the axial point is imaged by a large aperture beam, the beam of light emitted through the lens will no longer intersect a little, then the image of a single point can get a comma-shaped, such as comet, so called "Hui-poor".
2, like scattered
Astigmatism is also the difference in the color of an axis that influences clarity. When the field of view is very large, the point on the edge is far from the optical axis, the beam is tilted large, and the image is scattered after the lens. Like scatter the original spot after imaging into two separate and each other perpendicular to the short line, in the ideal image plane synthesis, forming an oval-shaped spot. Astigmatism is eliminated by complex lens combinations.
3, the field song
The field song is also called "like a field bend." When the lens exists in the field, the intersection of the beam is not coincident with the ideal point, although it can get a clear image point at each specific point, but the whole image plane is a surface. In this way, it is not possible to see the whole face at the same time in the mirror, causing difficulties for observation and photography. As a result, the objective of the microscope is generally a flat field objective, which has corrected the field.
The various differences in the above fields, except for the field curvature, affect the clarity of the image. Distortion is another property of the difference, the beam's concentricity is not damaged. Thus, it does not affect the sharpness of the image, but makes it distorted like the original object, in shape.
(1) When the object is located in the lens object twice times the focal length, then in the image square twice times the focal length, the focus is formed to reduce the inverted real;
(2) When the object is located at twice times the focal length of the lens, the same size of inverted real is formed on the twice-times focal length of the image square;
(3) When the object is located within twice times focal length of the lens, and outside the focal point, a magnified inverted real is formed outside the focal length of the image square twice times;
(4) When the object is in the focal point of the lens, the image cannot be imaged;
(5) When the object is within the focal point of the lens, the image is not formed, and the same side of the lens side forms a magnified upright virtual than the object in the far position.
The imaging principle of a microscope is to magnify an object using the laws of the above (3) and (5). When the object is in the front of the objective lens f-2f (F for the object focal length), then the twice times focal length of the objective image is formed to enlarge the inverted real. In the design of the microscope, this image falls within the eyepiece's 1 time-fold focal F1, the first image (middle image) magnified by the objective lens is once again magnified by the eyepiece, eventually forming an enlarged upright (relative middle) virtual in the object side of the eyepiece (the same side of the center image) and the apparent distance (250mm) of the human eye. Therefore, when we look at the microscope, we see the opposite of the image of the original object through the eyepiece (no additional conversion prism).