We are familiar with the term telescope, and I believe many people have played it, but do you really understand telescope? Is the telescope really the bigger the multiple, the better?
Since the telescope is an instrument for observing the distance, its function is to magnify the target for observation while minimizing the loss of the original details of the object. That is: the ideal telescope should “magnify the target non-destructively, and truly restore the details.”
Many people think that the magnification of a telescope should be as large as possible. In fact, the magnification of a telescope is determined by many factors. The practice has proved that the most suitable telescope for handheld observation should be 6-10 times, and 7 or 8 times is the most. The telescopes on the market generally do not exceed 20 times. If several hundred times or several thousand times are marked, it is undoubtedly a fake. Why not make the multiple higher? In fact, there are no technical difficulties with high-magnification telescopes. Any high-magnification can be achieved as long as you want. However, high magnification will bring many negative effects. The first is brightness. The higher the multiple, the worse the surface brightness of the object. Because the area of the object is enlarged to be proportional to the quadratic magnification, the brightness drop will be very obvious. Of course, if the diameter of the telescope is large, the magnification can be higher, but the diameter of the handheld telescope is generally not more than 50mm. There is more importantly the jitter caused by the high magnification, the hand-held telescope will have a slight jitter, but this slight jitter is amplified It will become very obvious in the future.
Above 10 times, the shaking of the image has already made the human eyes unable to fully observe the details of the image, and the telescope’s resolution ability can be used. What’s the use of increasing the magnification of the telescope at this time? If the telescope can be fixed on a tripod for observation, the magnification can of course be higher, but for the telescope for observation on the ground, due to the aforementioned brightness and resolution constraints, the magnification will not be too high, otherwise the image It will be very dim and blurry. At the same time, the field of view is too small, making it difficult to find the target. The highest magnification I have seen for large binoculars used for ground observation is 60 times and the aperture exceeds 100mm. In recent years, anti-shake telescopes have also appeared abroad. They adopt electromagnetic stabilization technology to “stabilize” the image, so that handheld telescopes can also be used for high-power observation. Of course, the price of such telescopes is very high, and the volume and weight are also very high. Larger, so the application is not very wide.
The aperture of a telescope is one of the most important parameters of a telescope. The larger the aperture of the telescope, the higher the theoretical resolution will be (but note that in fact, the general handheld telescope is far from using the theoretical resolution or reaching the theoretical resolution, so The actual resolution is more important, which depends on the optical quality of the telescope), the higher the light-gathering power (brighter at the same multiple), but at the same time the volume and weight of the telescope will be larger, and the price will be higher. Telescopes are generally 20-50mm. However, it should be noted that some low-quality telescopes are blocked by prisms and have too small diaphragms inside, so the actual aperture is smaller than the nominal value. At the same time, the brightness of the telescope is also closely related to the quality and performance of the coating. A small but high-quality telescope can often perform more effective observations than a large and poor telescope.
The diameter of the telescope divided by the multiple is called the exit pupil diameter of the telescope, which is the diameter of the light beam that the telescope emits from the eyepiece. This value is generally not marked on the telescope, but it can be easily calculated. At the same time, you can also measure directly. Point the eyepiece of the telescope towards yourself, the objective lens is facing the bright place, and the eyepiece is a certain distance away from you. At this time, you can see a bright round spot. The diameter of the round spot is the exit pupil diameter of the telescope. The cut edges of the circle indicate that the prism is bad or not big enough. Knowing two of the telescope’s multiple apertures and exit pupil diameter can calculate the third, so we can use this to verify whether the telescope’s nominal rating is accurate. Most of the formal product specifications are very accurate. The exit pupil diameter of the telescope directly determines the surface brightness of the object seen by the telescope. The larger the exit pupil diameter, the higher the brightness, which is proportional to the square of the exit pupil diameter. But when the exit pupil diameter is larger than the human eye pupil diameter, some light does not enter the human eye and is wasted, and the effective aperture of the telescope becomes smaller. The pupil size of the human eye is 2-3mm in the sun and can reach about 7mm in the dark, and it varies from person to person and becomes smaller with age. Regarding how to measure the maximum diameter of one’s own pupil, please refer to pupil size measurement. On the other hand, the exit pupil diameter also has a certain impact on the comfort of observation. When the exit pupil is large, the pupil will not easily deviate from the exit pupil beam when the pupil is shaking or when the eyeball rotates, so it will be more comfortable. The exit pupil diameter of a telescope is sometimes referred to as the exit pupil, but this is easily confused with another indicator-the exit pupil distance, which refers to how far away the observer’s eyes must be from the last lens to see the entire field of view. A telescope with a long exit pupil (generally considered to be around 22mm is the best) is very helpful for the comfort of the observer, especially the observer wearing eyes.