The basic optical principles of microscopes
(1) Refraction and refractive index
Light propagates in a straight line between two points in a homogeneous isotropic medium. When passing through transparent objects of different densities, refraction occurs due to the different propagation speeds of light in different media. When light rays that are not perpendicular to the surface of a transparent object (such as glass) are emitted by air, the direction of the light rays changes at its interface and forms a refraction angle with the normal.
(2) Performance of lenses
Lenses are the most basic optical components that make up the optical system of microscopes, and components such as objective lenses, eyepieces, and condenser lenses are composed of a single or multiple lenses. According to their different shapes, they can be divided into two categories: convex lenses (positive lenses) and concave lenses (negative lenses).
When a beam of light parallel to the optical axis intersects at a point through a convex lens, this point is called the focal plane, and the plane passing through the intersection and perpendicular to the optical axis is called the focal plane. There are two focal points, the focal point in the object space is called the "object focal point", and the focal plane at that point is called the "object focal plane"; On the contrary, the focal point in the square space is called the "square focal point", and the focal plane at that point is called the "square focal plane".
After passing through a concave lens, light forms an upright virtual image, while a convex lens forms an upright real image. Real images can be displayed on the screen, while virtual images cannot.
(3) Five imaging laws of convex lenses
When the object is located outside the focal length of the lens, a reduced inverted real image is formed within the focal length of the image and outside the focal point;
2. When the object is located at a double focal length on the lens side, an inverted real image of the same size is formed at a double focal length on the image side;
3. When the object is located within two times the focal length of the lens, but outside the focal point, an enlarged inverted real image is formed outside the two times the focal length of the image;
When an object is at the focal point of the lens, the image cannot be formed;
When the object is located within the focal point of the lens object, the image is also formed without an image, and an enlarged upright virtual image is formed on the same side of the lens object further away from the object.
