Through mass production by companies like Meade and Celestron, these portable and versatile telescopes have become affordable and very popular. It is the most fundamental characteristic in comparing telescopes and binoculars with each other. Many of the other elements of a telescope must get larger in proportion to the aperture, which thus determines the overall size and weight of the instrument. Aperture determines how much light an optical system can collect and how much magnification it can sustain. Generally speaking, a larger aperture instrument can reveal dimmer objects and finer details than one with smaller aperture, but the larger instrument will cost much more and be less portable, other things remaining equal.
Greater aperture translates directly into greater light-gathering power.
Aperture is usually measured in millimeters, but inches are still a traditional unit for telescopes. Light-gathering power increases as the square of the diameter, or aperture, of the instrument. An objective lens or mirror gathers light and forms an image in its focal plane. But an image can be magnified too much. Assuming good quality optics, a handy rule of thumb is that the maximum useful magnification is approximately 50x per inch of aperture.