Question

Why aperture in the telescope is made of larger size?

Answer 1

If the apertures were the same, there would be no light amplification. The objective lens or primary mirror of a telescope collects light over a large area (it’s aperture) and concentrates it on a small area where the eyepiece focuses and magnifies the image.

The aperture of an eyepiece is not to be confused with it’s focal length. The focal length is specified in mm and determines the magnification. The magnification is calculated as the focal length of the telescope divided by the focal length of the eyepiece. So against intuition, the shorter the focal length of an eyepiece the higher the magnification!

The aperture of an eyepiece is basically the diameter of the eyepiece barrel, which is either 1.25 inches or 2 inches for most telescopes (some other sizes also exist but are rare).