Question

can you explain the focal length of a telescope with a diagram in both refracting and reflecting telescope

Answer 1

A simple working telescope requires nothing more than a pair of lenses mounted in a tube. The lens in front, known as the objective lens, focuses an image; the lens in back, known as the eyepiece lens, magnifies that image. Although it may seem like a crude device, a simple telescope nicely illustrates the basic working principles of more powerful astronomical instruments.

LENSES

Light normally moves in straight lines, but there are situations in which this is not true. You are already familiar with some: for example, the distortions you see looking through the surface of the ocean occur because light bends as it passes from the water into the air. Long before we understood why light bends as it passes from one transparent material to another, people had used this effect to create lenses: optical devices which can gather light together or spread it apart.