An optical sight has at least three optical lens groups, one is an objective lens group (Objective lens), one is a correction mirror tube group (Erector YouTube), and an eyepiece group (Onicular lens), and possibly other mirror groups. The lens group is responsible for gathering light, so the larger the objective, the sights in the sight should be brighter, and the eyepiece Group is responsible for changing the light back to the parallel light, allowing the eye to focus and create the largest field of vision, while the corrective mirror tube group corrects the image of the objective lens from upside down, backwards and right to correct direction and is responsible for adjusting the magnification. The position of the aiming line can be in the first focusing plane before the correction Mirror Group, or the second focus plane, and the adjusting knob, the high-low adjustment button and the magnification ring are used to control the left and right, the height and the position of the correction mirror tube group. There may be as many as 9 lenses in the body of an advanced sight lens, and the transmittance may exceed 95% through proper coating. However, even if the light transmittance is not so high, the brightness in the field of vision may be higher than the naked eye, because the general objective lens area is larger than the eye area of light.