Unlike a lens, a mirror can be very thin. It would be like looking through a dirty window.Ī telescope that uses mirrors is called a reflecting telescope. Any flaws in the lens will change the image. Also, as they get thicker the glass stops more of the light passing through them.īecause the light is passing through the lens, the surface of the lens has to be extremely smooth. Heavy lenses are hard to make and difficult to hold in the right place. If you want to see far away, you need a big powerful lens. People with especially poor eyesight need thick lenses in their glasses. In a telescope, it makes faraway things seem closer.Ī simple refracting telescope uses lenses to make images bigger and more visible. In eyeglasses, this makes things less blurry. It’s hard to make a perfect mirror, but it’s even harder to make a perfect lens.Ī telescope made with lenses is called a refracting telescope.Ī lens, just like in eyeglasses, bends light passing through it. If they do have such problems, the image gets warped or blurry and is difficult to see. They can’t have any spots, scratches or other flaws. That means the mirrors and lenses have to be just the right shape to concentrate the light. The optics of a telescope must be almost perfect.

That light is what we see when we look into the telescope. Light is then concentrated by the shape of the optics. The bigger the mirrors or lenses, the more light the telescope can gather.

To do that, the optics-be they mirrors or lenses-have to be really big. The mirrors or lenses in a telescope are called the “optics.” Really powerful telescopes can see very dim things and things that are really far away. So why do we use mirrors today? Because mirrors are lighter, and they are easier than lenses to make perfectly smooth. The first telescopes focused light by using pieces of curved, clear glass, called lenses. Most telescopes, and all large telescopes, work by using curved mirrors to gather and focus light from the night sky. A telescope is a tool that astronomers use to see faraway objects.

Largest optical telescope