For telescopic sights, there are two types. The first focal plane and the second focal plane. The reticle of the first focal plane is located at the focal length of the objective lens, and the reticle of the second focal plane is located at the focal length of the eyepiece. The difference between the two is that the reticle of the first focal plane seems to be on the target. When the magnification is increased, the reticle is also enlarged. At the highest magnification, the reticle crosshair will become very thick. The advantage is that the reticle is fixed and easy to use. To correct, the disadvantage is that when the magnification is high, the thick front sight will block the target. The reticle of the second focal plane will not change according to the magnification. No matter how you zoom in, the reticle will look the same. The advantage is that the farthest sight will not become thicker when zoomed in. The disadvantage is that the reticle interval is different when the magnification is different. To be recalculated according to the current magnification.
The biggest difference between a firearm sight and a telescope is that it has strict requirements for shock resistance and maintaining mechanical accuracy. Every improvement in the optical and precision performance of the sight and the increase in function are all based on the increase in the size and number of lenses, and the complexity and precision of the adjustment mechanism. For example, to realize the zoom function, it is necessary to add a zoom lens and a mechanical structure to control it to move back and forth along the optical axis on the basis of the fixed-magnification sight. The harsh working conditions of high-strength impact have not changed, but the mechanical parts of various adjustment mechanisms are becoming more and more thin, and the loads they have to support are also getting higher and higher; this will inevitably affect the optical industry and precision machining belts. increasingly higher demands.