introduce
Binoculars zoom in on distant objects or zoom in on distant objects, so as to achieve telephoto and be able to see more details of distant objects. Here is a frequently asked question, that is, how far can the telescope see? Most of the people who ask this kind of question are novice Xiaobai or have not yet started, so I think it is necessary to explain, and then introduce them in detail.
Ask how far you can look with binoculars, depending on what you want to look at. If the object you look at is large enough and bright enough, you can see it at any distance. But if you want to see more details, then there will be many limiting factors.
The simplest explanation is that people look at people. If this person is next to you, then you can easily see who he is. But if this person is standing in a crowd one kilometer away, then your identification will become very difficult, because the facial details have been lost or can't be seen clearly.
How far can the telescope see?
Before explaining this question, we must first see how far the human eye can see? If you look into the distance with the naked eye, there are actually no restrictions, except below the horizon. If you raise your glasses and point to the sky, then the moon can be seen. You must know that the moon is actually quite far away. Of course, there are countless stars, you must know that they are far beyond human imagination.
Therefore, if the object to be observed is not obscured, if it is large enough, if it can emit light or reflect light, it can theoretically be seen with the naked eye, and the telescope can also see it naturally. But does it seem that there are no restrictions here?
Limiting factor
On the earth, how far you can see with a telescope or with the naked eye depends on two limiting factors: atmospheric conditions and the curvature of the earth (horizon). If you want to see the details of distant objects, it depends on the angular resolution.
Atmospheric conditions
This is easy to understand. Actually, it is what we usually call the weather. This factor will seriously affect how far we can see. If it is rain, fog, sandstorm, and other severe weather, it will definitely be different from wind and sunny weather. Even if it is sunny, there is a difference between a heavily polluted city and a beautiful suburb with good air quality. In short, your environment and weather conditions will affect or limit how far you can see, including looking with a telescope. Here we also need to borrow a concept of astronomical observations-seeing. This concept simply refers to the stability of the high-airflow, even if the weather is clear (viewed from the ground) and the seeing is not good (the high-airflow is unstable), use a telescope Seeing will also give you a very poor observation experience (mainly affecting stargazing).
horizon
This is actually very easy to understand. Everyone knows that the earth is round, so after a certain distance, there will be arcs on the surface. The most classic case is looking at a distant ship on the beach. If the ship is moving away from you, it is very likely that you will not be able to see the mast of the ship after a few kilometers, because it is already below your horizon.
Everyone must know the saying, stand tall and see far. If you are standing on the top of a mountain or a high tower, the distance you can see will be greatly increased. Everyone has an experience.
Angular resolution
If the first two conditions affect how far we can see, then the following factor directly affects how much detail we can see (this is usually asked how far we can see and how clearly we can see). How much detail can be seen depends on the resolution, more accurately the angular resolution of the human eye.
Angular resolution (also called resolution) is the ability to distinguish the structure of the target object. Simply put, it is the minimum distance that can separate the different structures of the object and treat it as a single part.
The resolution of the human eye in a relaxed condition is approximately one cent. This ability of the human eye ranges from a short distance (a few centimeters) to infinity. Unfortunately, this ability becomes weaker with age. When the object is far away, we can't distinguish the details of the object very well, because they look like they are all close together. Our glasses cannot separate them, so they look like one part (above).
Using optical instruments (telescopes, microscopes), we can zoom in on distant objects, so that distant objects look closer, and we can also see more details. But optical instruments also have laws. The Rayleigh criterion describes the shortest distance of the resolving power of an optical device. These are mainly related to diffraction, wavelength, and aperture. But in fact, you only need to remember that the larger the caliber, the better, the higher the resolution, and the more details you can see.
How far can you see with a telescope?
In nature, the farther the object is, the smaller it is, and the farther the object is to see more details, it needs more powerful resolution capabilities. This is why some astronomical telescopes have become bigger and bigger in recent years.
In practical applications, such as traveling with a telescope, climbing mountains, viewing scenery, etc., you also need to consider volume and weight. Generally speaking, it is 8-10 times and the diameter is between 30mm~40mm. This is also the point of balance in all aspects.
If you want to see farther, you need to consider a 12-15 times mirror, but because it is too heavy, you can no longer hold it, so you can only put it on the shelf for observation.
If you still don’t think you can see far enough, and you want to see farther and smaller objects, then you need to consider a bird-watching mirror or an astronomical telescope. However, this type of telescope is no longer portable, and can only be viewed with the help of a tripod. Of course, the price is directly proportional. Although astronomical telescopes or bird-watching mirrors have high magnification and a strong sense of pull-in, they are also more sensitive to the influence of the atmosphere, and the viewing angle will become very small when the magnification is increased, and various other optical problems will also appear, so I won't introduce them here.
