How Microscopes Work
An optical microscope consists of two sets of lenses (eyepiece and objective lens), each set of lenses is equivalent to a convex lens. The focal length of the objective lens is short, and the focal length of the eyepiece is long. Working principle: The object first passes through the objective lens to form a magnified real image, and then passes through the eyepiece to form a magnified virtual image. After the second magnification, tiny objects can be seen clearly.
(1) Refraction and refractive index
Light travels in a straight line between two points in a homogeneous isotropic medium. 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) The performance of the lens
Lenses are the most basic optical components that make up the microscope optical system. Components such as objective lenses, eyepieces, and condensers 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 the "focus point", and the plane passing through the intersection point and perpendicular to the optical axis is called the "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 light passes through a concave lens, it forms an erected virtual image, while a convex lens forms an erected real image. Real images can be displayed on the screen, while virtual images cannot
(3) Five imaging rules of convex lens
1. When the object distance is beyond the double focal length of the object side of the lens, 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 distance is twice the focal length on the object side of the lens, an inverted real image of the same size will be formed on the image side twice the focal length;
3. When the object distance is within twice the focal length of the object side of the lens and outside the focal point, a magnified inverted real image will be formed outside the double focal length of the image side;
4. When the object distance is at the focal point of the lens object, the image cannot be imaged;
5. When the object distance 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.
