For such objects, a focal ratio of f/10 or more is ideal. But if you want to see wide views of star clusters, galaxies, and the Milky Way, a lower focal ratio is better. You get less magnification, but you see more of the sky. Wide field telescopes have a focal ratio of f/7 or less.

Telescopes have opened our eyes to the universe. Early telescopes showed that Earth was not the center of the universe, as was previously believed. They also showed mountains and craters on the moon. Telescopes have also helped us understand gravity and other fundamental laws of the physical world.

The shape of the mirror or lens in a telescope concentrates light. That light is what we see when we look into a telescope. A telescope is a tool that astronomers use to see faraway objects. Most telescopes, and all large telescopes, work by using curved mirrors to gather and focus light from the night sky.

Minimum and Maximum Aperture of Lenses A lens that has a maximum aperture of f/1.4 or f/1.8 is considered to be a “fast” lens, because it can pass through more light than, for example, a lens with a “slow” maximum aperture of f/4.0. That’s why lenses with large apertures usually cost more.

A good all round first telescope should have a focal length of around 1000mm to 1200mm. All refracting telescopes use a glass lens as their primary focusing unit.

Barlow lenses are concave or negative lenses that amplify or magnify the image produced by your telescope. They work by lengthening the converging cone of light from the scope, effectively increasing its focal length.

50x magnification

Those are the five brightest planets, but in reality, there is a sixth planet that can be glimpsed without the aid of either a telescope or binoculars. That sixth planet is the planet Uranus.