(1) Refraction and refractive index
light travels in a straight line between two points in a uniform isotropic medium. When it passes through transparent objects with different density media, refraction occurs, which is caused by different propagation speeds of light in different media. When the light not perpendicular to the transparent object surface enters the transparent object (such as glass) from air, the light changes direction at its interface and forms a refraction angle with the normal.
lens is the basic optical element constituting the optical system of microscope. The components such as objective lens, eyepiece and condenser are composed of single and multiple lenses. According to their different shapes, they can be divided into convex lens (positive lens) and concave lens (negative lens).
when a beam of light parallel to the optical axis passes through the 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 focal point in the object space is called "object focal point", and the focal plane there is called "object focal plane"; On the contrary, the focus in the image square space is called "image square focus", and the focal plane there is called "image square focal plane". After the light passes through the concave lens, it becomes an upright virtual image, while the convex lens becomes an upright real image. The real image can be displayed on the screen, while the virtual image cannot.
