Light grasp

Also called: light-gathering power, light gathering.

How much more light a telescope collects than your eye: (aperture ÷ 7 mm)². An 8-inch gathers about 840×.

Light collected grows with the area of the aperture, so it goes with the square of the diameter. A 200 mm telescope collects about 840 times as much light as a 7 mm dark-adapted pupil — reaching about 7 magnitudes fainter.