1 Basic optical principles of microscopes
(1) Refraction and Refractive Index
In a uniform isotropic medium, light travels in a straight line between two points. When it passes through transparent objects with different densities, the phenomenon of refraction occurs, which is caused by the different propagation speeds of light in different media. When light rays that are not perpendicular to the surface of the transparent object are injected into the transparent object (such as glass) from the air, the light rays change their direction at the interface and form a refraction angle with the normal.
(2) The performance of the lens
The lens is the most basic optical element that constitutes the optical system of the microscope. The objective lens, eyepiece, condenser and other components are composed of 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 rays parallel to the optical axis passes through the convex lens and then intersects at a point, this point is called the "focal point", and the plane passing through the intersection 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 focal plane"; on the contrary, the focus in the image space is called "image focus". The focal plane at the focal plane is called the "image square focal plane".
When light passes through a concave lens, it forms an upright virtual image, while a convex lens forms an upright real image. Real images can appear on the screen, but virtual images cannot.
