Objective lens: the objective lens is at the front end of the sight, which is the part of the sight to receive external light source. The larger the diameter of the objective lens, the more light source it can receive. At the same distance, the larger the diameter of the sight, the clearer the image the shooter can see. Usually, in order to obtain more lighting, manufacturers will coat a layer of fluoride on the surface of the objective lens to improve the light transmission and reduce the reflection (see physics compulsory for high school for details). If you see purple or yellow reflection in the objective lens, needless to say, it is the reflection caused by coating.

The diameter of the objective also determines the exit pupil diameter of the sight. What is the exit pupil diameter? We know that the sight will produce an image behind the eyepiece, and the diameter of the image is the diameter of the exit pupil. Exit pupil diameter = objective lens diameter / magnification under normal circumstances, the exit pupil diameter is not less than 5mm, because this is the size of the pupil of our eyes. If it is too small, we can not see a complete and clear image. Under low light level conditions, the pupil of a person is enlarged to 8mm, so we can obtain a larger exit pupil diameter by adjusting the magnification of the sight.

Adjusting hand wheel: the adjusting hand wheel is located in the middle of the lens barrel. The upper one is the pitching hand wheel, which has BDC (trajectory altitude correction knob) and target correction knob. The only difference between the two is that the scale indication of the target correction knob is smaller; the right one is the direction hand wheel of the sight, which is used to adjust the horizontal direction to correct the wind deviation and the advance of the moving target; the left one is the direction hand wheel By adjusting the focusing hand wheel of the objective lens, the image can be clearer and the error can be reduced. Of course, some of the sight is through the focusing ring.

Inverted image group: we know that when the convex lens is out of the double focal length, what we see is the inverted and enlarged real image, while the eyepiece is too small to the pupil, what we see is the enlarged virtual image, so if there is no inverted image group, what we see from the eyepiece is the enlarged and inverted image. It's very inconvenient for aiming. And the inverted image group is to play the role of putting the image right.

Mirror barrel: the mirror cylinder is used for mounting in inverted image group and adjusting handwheel and other parts, which plays the role of protection and light passing. The diameter of the barrel is about 1 inch, and that of the European sight glass is about 30mm. The larger the barrel, the greater the brightness of the light, the lower the refraction angle, so that the image will be clearer.

Eyepiece: the eyepiece is located at the last end of the sight. The function of the eyepiece is to further enlarge the image magnified by the objective lens and transmit it to people's eyes. Generally speaking, the diameter of the eyepiece is small, only slightly larger than the barrel, which is determined by the role of the eyepiece. Eyepiece focal length and diameter determine the exit pupil distance of the sight, that is, the shortest distance from the imaging plane to the eyepiece. The exit pupil distance generally varies from 5 to 10 cm, which is to avoid the sight hitting the eye socket because of recoil when shooting. As the exit pupil distance is fixed, the appropriate exit pupil distance should be adjusted when the sight is installed. Once the adjustment is completed, the shooter can quickly obtain the maximum field of view and clear image when aiming according to the gun, and can also minimize the parallax.