Question

In telescope the objective has large aperture while the eyepiece has small aperture.why?

Answer 1

That’s usually true because the function of the objective is to collect a lot of light and form an image, and the function of the eyepiece is to allow the eye to inspect a portion of that image (the higher the magnification, the smaller the portion of the overall image that is inspected). The more light the objective collects, other things being equal, the brighter the image.