Basic knowledge of optical microscope
1. The basic optical principle of microscope
(1) Refraction and refractive index
In a homogeneous isotropic medium, light propagates in a straight line between two points. When it passes through transparent objects with different densities, refraction occurs, which is caused by the different propagation speeds of light in different media. When the light that is not perpendicular to the surface of the transparent object enters the transparent object (such as glass) from the air, the light changes direction at its interface and forms a refraction angle with the normal.
(2) Performance of the lens
The lens is the most basic optical element that makes up the microscope optical system. The objective lens, eyepiece and condenser lens are composed of single or multiple lenses. According to their 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 passes through a convex lens and intersects at a point, this point is called "focus", and the plane passing through the intersection and perpendicular to the optical axis is called "focal plane". There are two focal points, the focus in the object space is called "object focus", and the focal plane there is called "object focus plane"; on the contrary, the focus in the image space is called "image focus". The focal plane at is called the "image square focal plane".
After the light passes through the concave lens, it forms an erected virtual image, while the convex lens forms an erected real image. Real images can appear on the screen, but virtual images cannot.
(3) Five imaging laws of convex lenses
1. When the object is beyond the double focal length of the lens object side, a reduced inverted real image will be formed within the double focal length of the image side and outside the focal point;
2. When the object is on the double focal length of the object side of the lens, an inverted real image of the same size will be formed on the double focal length of the image side;
3. When the object is within twice the focal length of the lens object side and out of focus, a magnified inverted real image will be formed outside the double focal length of the image side;
4. When the object is on the focal point of the lens object, the image cannot be imaged;
5. When the object is within the focal point of the lens object side, no image will be formed on the image side, and a magnified upright virtual image will be formed on the same side of the lens object side as it is farther from the object.
