Recommend a pair of binoculars. Can be used for astronomical observation.

What kind of telescope do you need? Selection of astronomical binoculars

Here, I will roughly explain some questions about binoculars, which may not be completely correct, but if you can read and understand these things patiently, I believe you can already know the choice of binoculars.

It is not difficult to understand that we must know some important parameters and characteristics of binoculars in order to know fairly well. Here, we mainly focus on astronomical binoculars.

1 exit pupil diameter

I put this in the first place to measure whether a binocular is suitable for astronomical observation. Usually I look at this parameter first, which is the most important and core parameter in astronomical binoculars. Knowing this parameter and its significance can solve more than half of the problems, so I want to say more here.

The diameter of the exit pupil is the round bright spot on the eyepiece, and its diameter determines the sensory brightness of both eyes. You can actually measure it with a plastic transparent ruler, or through simple specification calculation. Its calculation formula is: objective aperture (MM)÷ actual multiple = exit pupil diameter (MM). It can be seen that the third value can be calculated by knowing any two parameters, so the real multiple can be calculated by detecting whether your multiple is a virtual standard and measuring the diameter of the objective lens and the bright spot of the pupil. Because people's pupil diameter is generally less than 7MM, the exit pupil diameter of both eyes is generally less than 7 mm, and the maximum pupil diameter of people will also decrease with age. On this premise, the larger the diameter of binocular exit pupil, the higher the sensory brightness. For example, some classic high-brightness binoculars are of such specifications: 7 (multiple) X50 (aperture) and 8X56. (Some binocular objective tubes may be inaccurate if a diaphragm or multiple dummy marks are added. )

So is the brightness of the astronomical telescope as high as possible? The answer is not necessarily, the specific situation needs to be treated specifically. Let me talk about how to choose the appropriate exit pupil diameter, because its value may determine the specifications of binoculars!

According to my practical observation experience, binoculars are more sensitive to large area surface light sources, but less sensitive to point light sources. Therefore, if you observe the landform of the ground target, the specifications of the exit pupil such as 7X50 will make you feel bright, while when you observe the near-point light source such as the starry sky, its sensitivity will not change much. So, if your observation environment is not ideal, or there is some light damage, then if you look at the sky with a pair of large-exit-pupil binoculars like 7X50 (I use my 7X50 and the same series and the same caliber 12X50 as examples): in 7X50' s field of vision, although there are many more stars, the sky background becomes much brighter, because of the light damage and the scattering of clouds and atmosphere. Point light sources such as stars are not so conspicuous because of their low sensitivity. If you switch to 12X50, you can clearly feel that the stars are still so bright, but the sky background turns black, so this kind of star is easier to distinguish. The diameter range of the exit pupil of the astronomical binoculars I personally gave is 4-7 mm, 7 is the upper limit, generally there is no bigger one, and 4 is the lower limit. Of course, if it is a poisonous mirror, the lower limit can be slightly lowered due to the high light transmittance of the material, so the suggestions are as follows:

1) If your observation environment is absolutely good enough, then this large exit pupil mirror can play a very good role.

2) If your observation environment is not ideal or there is a little light damage, then this large exit pupil mirror may not bring you the strength it deserves, and the effect is not even as good as some smaller exit pupils. The value of exit pupil diameter can be appropriately reduced, of course, it cannot be lower than the lower limit. As can be seen from the above formula, if the exit pupil value changes, the specifications will also change. There are two options, one is to reduce the aperture, but the smaller aperture will theoretically reduce the resolution of the mirror, or increase the magnification, but the magnification. In this case, other specifications will be more suitable, such as: 10x50, 12x50, 8x40, 8x45, 7x40 and so on.

As can be seen from the above, 7X50 is a good specification, because its specifications are easy to make good optical effects, but it can't be obsessed, let alone mythical. It also has many limitations, and is suitable for the following environments: small jitter, suitable for ships, astronomical survey, high brightness in low light environment of surface light source, suitable for patrol, mountain patrol and star observation in excellent environment.

The reason why so many words are used to talk about pupil diameter is because it is the most important parameter in astronomical binocular parameters. Let's talk about other parameters.

A multiple of 2

The diameter of the exit pupil is fixed, so the multiple and aperture basically determine their range. I put multiples in the second place because they also play an important role in astronomical observation. The observation targets of astronomical binoculars are suitable: constellations, magnificent galaxies and deep space objects. They need different multiples. We know that the higher the magnification, the smaller the field of view (discussed in detail below), that is, the smaller the field of view actually seen through the telescope, so we need to look at the constellations and browse the Milky Way with low magnification and large field of view. For deep space objects, because of the small apparent diameter and low brightness, high-power large-aperture mirrors are more suitable.

According to the range of exit pupil diameter determined above, we can roughly get the specifications and caliber we need according to the multiple. For example, when looking at constellations and the Milky Way, it is enough to choose a mirror 4-6 times. According to the set range of exit pupil value, the aperture within 30 is basically enough, and generally, their visual field is relatively large, which brings the advantage that the volume and weight are obviously reduced, and it is easy to carry and can be picked up anytime and anywhere. Of course, 7X50 can also be used to look at constellations or something, but it is not suitable. Its 50 caliber is very heavy, and its field of vision can't be as big as those small mirrors.

For observing deep space objects, 12-25 times is more appropriate. According to the minimum exit pupil diameter of 4MM, the aperture should be within 50- 100. The higher the multiple, the larger the aperture, and it is very difficult to keep it within 15 times. So in this range, we can also see many classic specifications suitable for deep space, such as 12x50, 12x60, 15x60, 15x70, 20x80, 25x 100. Can we calculate whether their exit pupil diameters conform to the law of about 4MM or more?

As you can see, when looking at constellations and the like, you can choose a large field of vision with low magnification, and when looking at deep space, you can choose a large aperture with high magnification, or you can put the big one in your pocket with a small one, which is basically suitable for all astronomical binocular occasions. If there is only one condition, it is recommended to choose from the specifications of 7x50, 8x40, 8x45, 10x40, 10x50. These specifications are moderate, taking into account both ends, although neither end is the best.

3 caliber

When the above two parameters are determined, the caliber is basically determined. Let me talk about the caliber and resolution first (both are my own feelings). According to the theoretical calculation formula, the theoretical resolution of the telescope depends on the aperture of the objective lens, but the resolution provided by the objective lens far exceeds the resolution of the human eye for 60 seconds, so we need to use an eyepiece to enlarge it. Although we feel the scene is clear at low magnification, we may not be able to give full play to the resolution provided by the objective lens. Appropriately increasing magnification can improve human perception of resolution. Let's use my 7X50 and 12X50 to illustrate (because they are of the same series, the same caliber and the same brand, which is more telling). Looking at the words on the blackboard at the same distance, 12X50 is obviously easier to recognize. 7X50 has a sharper sense, but the actual resolution is not as good as 12X50. This may be the reason I mentioned above. Remember the north. But there is a limit to the improvement of this multiple. After all, such a large objective lens can only provide us with such a strong resolution. In the selection of astronomical binoculars, the diameter of the front exit pupil has been limited by multiple, so we basically don't have to consider this problem, which is one of the reasons why I put the diameter of the exit pupil in the first place.

In deep space observation, some celestial bodies, such as globular clusters and open clusters, can be better decomposed and more details can be obtained at higher magnification.

4 field of vision (there are simple calculation and conversion formulas, you can skip them if you don't like them)

I have said a little about the previous vision, and there is a lot to say about this problem. I'll just pick the main ones here.

Ordinary amateurs divide the visual field parameters into two types. One is the actual field of view, and the other is the apparent field of view.

1) on binoculars is generally marked with the actual visual angle, and some are marked with XXm/ 1000m (i.e. XX m/1000 m, which can be converted, which will be introduced below), showing what can be seen in the binocular visual field at the distance of 1000m.

2) The apparent field of view is the circle of the field of view seen by the human eye from the telescope, and its size or the degree close to the human eye can also be said to be the opening angle. The bigger the circle, the closer it is to the human eye, which means that the larger the apparent field of vision, the stronger the immersion of the human eye. There is also a simple formula for calculating apparent visual field: actual visual field angle × multiple = apparent visual field. Generally, a wide angle is above 60 degrees, and a super wide angle is above 70 degrees. For example, the actual field of view of a 7X50 binoculars is 7 degrees, and the apparent field of view of 7× 7 = 49 degrees is far wide angle, while the actual field of view of another 10X42 is 6.5 degrees, which is less than 7X50, but its apparent field of view reaches 65 degrees wide angle. Therefore, in actual observation, this 10X42 field of view circle will be larger and closer than 7X50. It is best to watch and browse the Milky Way with low magnification and wide angle, 7X50 is not suitable.

3) Some simple calculation formulas and conversion formulas of field of view parameters.

Some actual viewing angles are directly marked on the mirror, some are marked by domestic marking methods: XX m/ 1000 m (that is, XX m/ 1000m), and some are marked by English marking methods: XX ft/ 1000 yds. These marking methods all need to calculate the number of view angles, and the calculation is very simple:

Marked as XX ft/ 1000 yds, such as 366ft/ 1000yds, you can directly divide 366 by a constant of 52.5 to get the actual viewing angle: 366÷52.5=6.9 degrees (approximate value). Is it very simple?

Marked as XX m/ 1000 m, such as 207m/ 1000m, directly divide 207 by the constant 17.5, and you can get the actual viewing angle: 207 ÷17.5 =1/kloc.

Suggestions on selecting visual field parameters:

If it is used for sightseeing, try to choose a wide angle and a moderate multiple. Wide-angle and ultra-wide-angle sightseeing have a feeling of being a person in a painting. If you are looking at a constellation or the Milky Way, try to choose low-power wide-angle binoculars and enjoy the feeling that the stars are coming at you.

However, there is a problem that needs to be recognized here. Generally speaking, the image quality and distortion of wide-angle and ultra-wide-angle mirrors are obviously worse than those of narrow-angle mirrors. If the star points at the edge of the field of view will be blurred or dragged out of the small tail during star watching, there is generally no good way, and the top mirror can only minimize this aberration.

5 coating

Many people have a coating plot. Many Taobao merchants say that green film is better than blue film, and blue film is better than red film. In fact, the blue film has no chromatic aberration. I wonder if he knows what color difference is. This is actually incorrect. The original intention of coating is to improve light transmittance, brightness and correct some chromatic aberration. The same quality, the coating color is not good or bad, but the imaging style is different. The famous Zeiss has a red film. Sample. Aside from the influence of glass material, as far as single-layer coating is concerned, according to the principle of three primary colors, red coating will increase the green-blue transmittance of red, green and blue, so the image will become blue or cyan, blue coating will increase the red-green transmittance, yellow imaging will be yellow, green coating will increase the red-blue transmittance, and the image will be purple or magenta. Therefore, the double-tube coating with slightly higher grade is generally broadband ultra-wideband coating, which can improve the transmittance of light with multiple wavelengths (light also has a certain wavelength), so the brightness will be higher than that of single-tube coating, but both of them are broadband coating with different quality.

So what kind of coating is good? How to roughly distinguish? Look at the degree of reflection and point the coating at the light. If we can see the details in the lens barrel more clearly, the coating quality is better. Those coatings that can only see your face show strong reflection, low transmittance and poor quality, and the brightness is definitely not as good as that of transparent coatings. There is actually a lot about coating, so I won't say much here.