What is a lens?

The lens is the most basic optical element that composes the microscope optical system. Components such as objective lenses, eyepieces and condensers can be composed of single or multiple lenses.

Lenses are divided into convex lenses and concave lenses.

When a beam of rays parallel to the optical axis passes through a convex lens and 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"; conversely, 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.