Theoretical knowledge of telescope multiples
The magnification of a telescope is the angular magnification of the angle of observing an object with the naked eye and the angle of observing the same object with the telescope at the same place. For example, if the angle of a bird to the naked eye is 6 arc minutes, and the angle of observation with a telescope is 60 arc minutes, the magnification of the telescope is 10 times. The above is a theoretical explanation. The most straightforward explanation is that an object with a height of 0.1 meters can be seen with the naked eye, and a telescope with 10 times the height can be seen at a height of 1 meter.
How is the magnification of the telescope calculated?
Multiplier = focal length of objective lens/ focal length of the eyepiece.
If the telescope does not indicate the focal length of the objective lens, you can actually measure it. For example, measure the diameter of the sun’s image and calculate it based on the sun’s focal length of 8.7mm per meter. In addition, the focal length of the objective lens can generally be estimated from the length of the lens barrel. For some telescopes with special structures, the light path may be refracted by the internal prism or flat mirror, which will shorten the length of the actual lens barrel. The roof-shaped refraction is not easy to observe even from the outside. Observe it on. In addition, due to the special structure of the telephoto lens, although there is no reflection, the length of the lens barrel can be much smaller than the focal length.
What are the negative effects of too high a telescope’s magnification?
1. If the telescope’s multiple is too large, it will cause the image to shake.
Hand-held binoculars are generally 7-10 times better. When you observe the scene more than 10 times, they will shake badly. Because of the shaking of the image, it is not conducive to observing the details of the image. It will cause dizziness, eye fatigue, and even nausea. If the fixed telescope is too large, it will cause vibration due to wind and grass. For the observer, 12 times is the limit multiple of the handheld telescope, and it is best to have the elbow support when observing, and the body or the telescope should be attached to some fixed objects. In theory, a tripod must be used for telescopes 12 times or more.
2. The telescope magnification is inversely proportional to the field of view.
Generally speaking, the larger the multiple, the smaller the field of view, which means that the observable area will be smaller. This is not just because of the eyepiece. Even if the eyepiece can maintain the same apparent angle of view (for example, 60 degrees) when the focal length changes, the field of view will decrease inversely proportional to the magnification due to the reduction of the observation area. In this way, it is not conducive to discovering and searching for targets, and it is especially unfavorable for observers who frequently change targets. Even if the target is found, it is easy to lose the target if the shelf shakes a little. One point that needs to be explained, the multiple of the telescope is only a factor that affects the field of view. Different styles of telescopes have different internal designs. Even with the same caliber and the same magnification, the field of view (field of view) is quite different.
3. The magnification of the telescope is inversely proportional to the brightness of the telescope
For example, when the aperture is 50mm, the brightness (index) is 50 when 7 times, 10 times in 25, 15 times is 11, and 25 times in 4. The reduction of the brightness of the object will directly affect the observed effect of the human eye (the resolution ability of the human eye) , Color ability becomes worse and worse with the decrease of brightness). Generally speaking, when the brightness during the day is less than 5 and the brightness at night is less than 20, it is difficult to observe dim objects. Large-aperture telescopes have advantages at this point. For example, a mirror with a diameter of 300mm, when magnified by 50 times, the brightness is still 36 (very bright). In addition, when observing bright celestial bodies in the solar system, they are basically not subject to this limitation due to their high brightness. Of course, the brightness of the telescope is not only related to the multiple of the telescope, but also related to the coating and lens of the telescope, and the internal optical path structure.
4. Too high telescope magnification will result in a small exit pupil distance
The acquisition of large magnifications is generally done through short focal length eyepieces. The short focal length of the eyepiece will result in a small distance between the lens and the eye (that is, the exit pupil distance), a small viewing angle, and other problems, resulting in uncomfortable observation and unsuitable use for glasses wearers.
How to choose a binocular multiple that suits you?
1. As an ordinary consumer, when choosing binoculars, whether you are traveling outdoors or watching games indoors, you should not choose binoculars that are more than 10 times larger. Because the brightness coefficient of large-magnification binoculars is too low, there are basically no real high-definition telescopes for binoculars above 10 times.
2. Telescopes of more than 10 times are only suitable for special groups of people and need to be equipped with a triangle for use.
3. For indoor use, it is generally appropriate to use a 7-fold telescope.
4. For outdoor use, it is generally suitable to use 8-10 times binoculars.
5. If you need to carry it conveniently, it is recommended to buy a small-aperture telescope within 32mm. This type of telescope is small in size and generally weighs less than 400 grams. When choosing a small-aperture mini telescope, you must choose a high-definition level, and you must also pay attention to the size of the field of view.
6. If you use it outdoors, you can choose some telescopes with a larger aperture, such as 42mm or 50mm.
7. If it is 8-10 times, should you choose an 8 times telescope or a 10 times telescope? This can be determined according to personal preference. If you like a larger field of view, choose 8 times, and if you like a long distance, choose 10 times.