Why do telescopes use gratings?

Grating is a device installed in front of photographic lens, digital camera and video camera to block harmful light, and it is also one of the most commonly used photographic accessories. The hood is made of metal, hard plastic, soft rubber and other materials. Most 135 lenses come standard with a hood, and some lenses need to be purchased separately. Different lenses use different models of hoods and cannot be used interchangeably. The hood is an indispensable accessory of visible light lens.

Telescope magnification: The magnification of a telescope refers to its ability to magnify objects. For example, when observing an object with a 7-fold telescope, the effect of observing an object at a distance of 700 meters is similar to that of observing it with the naked eye at a distance of 100 meters (of course, the effect is worse due to the influence of environment, light and weather).

The exit pupil diameter of the telescope is the spot size formed on the eyepiece after the image passes through the telescope. The exit pupil diameter can be obtained by the following formula: objective lens/magnification = exit pupil diameter. It can be seen that the larger the objective lens, the lower the multiple and the larger the exit pupil diameter.