A telescope is a device that helps you to look to far distances, some of even enabling to look to thousands of kilometers. Telescopes are mainly used for astronomic purposes in science, like searching for new planets and solar systems and investigating the ones already know to man. But also usual people and especially some students are keen on looking and exploring the wide spaces in sky on their own with a weaker telescope, without any extra assistance.

An optical telescope is an optical tool that collects and focuses electromagnetic radiation. The effect on the telescope is that it increases the angular size of far away objects and therefore makes them viewable and telescopes also increases the apparent brightness of the image viewed. A telescope works by using one or even more curved optical elements- mirrors or lenses- to collect light or other electromagnetic radiation and brings that light or gathered electromagnetic radiation to a focus, which means that an object can be observed, studied or even photographed.

Telescopes do not form perfect image.

Even if perfect mirrors were in reflecting telescope or a perfect lens in refracting telescope, the effects of aperture diffraction is still inevitable. Actually in reality, perfect mirrors and perfect lenses do not exist, so image peculiarity in addition to aperture diffraction must be considered.