Is the larger the field of view of the telescope the better?

Telescope parameters When people buy telescopes, they often see several Arabic numerals on the price list. So what technical parameters do these numbers indicate? Let’s give an example to illustrate. For example, if it is marked 10×50mm5°, it means that the magnification is 10 times, the diameter of the objective lens is 50 mm, and the field of view is 5 degrees (that is, the field of view width at 1000 is 87.4 meters). Some people may think that the larger the technical parameter number, the better, but this is not the case. Magnification is inversely proportional to the width of the field of view, that is, the greater the magnification, the smaller the width of the field of view, which is not conducive to search. The larger the diameter of the objective lens and the amount of light entering, the stronger the resolution when the light is insufficient, but this will inevitably lead to an increase in the size of the telescope, which is not convenient for portability. Having said this, you may feel at a loss as to what to do, but as long as you can learn from each other's strengths and weaknesses, you can still buy a satisfactory telescope. Here I would like to give you some suggestions for your reference when purchasing telescopes:

First, if you want to travel to the sea or the beach, please don’t forget to buy a waterproof telescope (especially recommended) Debao offshore series 7×50mm waterproof telescope made in the United States).

Second, if you want to go out for sightseeing, you can buy a small telescope with a zoom function.

Third, if you plan to go hunting in dangerous areas that can be viewed from a distance but cannot be explored up close [1], you should buy a high-power telescope.

Chapter Fourth, if you want to go hunting or travel for a long time, it is best to buy a variable magnification telescope. Now I will explain how to use it. Because the variable magnification telescope can be gradually adjusted from low magnification to high magnification, you should first use it. Use low magnification and large field of view for a rough search, and then use high magnification and small field of view for careful observation.

The following is a description of the collected telescope parameters

For those who like to do research, take a look.

Purchasing a satisfactory telescope is a very important issue for users, because it determines whether the telescope can well meet their own needs. However, beginners often do not have telescopes. Identification and related optical knowledge, especially in the current situation where there are a lot of inferior telescopes on the market, how should beginners choose a telescope? In response to the confusion of friends, the author combined his many years of telescope production and sales experience and Based on my understanding of the domestic telescope market, I compiled this article, hoping it will be helpful to everyone, especially newbie friends:

1. Decide the optical system structure and magnification range of the telescope according to your own use

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The ultimate goal of buying a telescope is comfortable use, so determining the main purpose is crucial and is the first step in purchasing. It determines the subsequent steps. It is conceivable that if it is mainly for watching sports games, then If you choose a large telescope with a PCF structure, it will feel heavy and bulky in actual use. Your wrist will get sore after being lifted for a long time, and you will not be in a good mood to watch the game.

In addition, the magnification is not too high. The bigger the better, because it magnifies not only your field of view, but also the shaking of your hands. Generally speaking, the most suitable magnification for hand-held observation on land is 6-12 times, and 6 -8x is the best. After 12x, due to the small field of view and small diameter of the entrance pupil, the shaking of the human hand is also multiplied, making hand-held observation more difficult. This is why most military telescopes are within this magnification range. (The magnification of some marine telescopes can reach 15 times to 20 times)

2. Pay attention to the difference between nominal parameters and real parameters

You may have noticed that the telescope usually has at least 15 times the magnification. Print two parameters like this: 8X21 131M/1000M, (the latter may be printed as parameters like 393FT/1000YDS, sometimes also printed as parameters like FILE=7°;, but this kind of printing is more complicated Rare), these are the most critical parameters of a telescope. The former represents the magnification and clear aperture of the telescope. For example, 8X21 represents the magnification of 8 times and the clear aperture of 21mm. And so on. If the printed parameters are 10X50 means that the magnification is 10 times and the clear aperture is 50mm. So knowing the meaning of this parameter, we can easily determine whether the printed parameters of a telescope are true. For ordinary fixed-magnification telescopes commonly available on the market, if the magnification If the printing exceeds 12 times, we should be skeptical (variable magnification telescopes can reach 15 times, 20 times, 30 times or higher magnification, such as the common specifications of 7-15X35, 8-24X50, 10-30X60, etc.), It is necessary to carefully evaluate whether it is true in combination with other parameters. If the printed magnification exceeds 20 times, we can basically determine that this is a false magnification. The determination of the clear aperture is relatively simple. Generally speaking, it is approximately the same diameter as the objective lens of the telescope (actually 1-2mm smaller, but it can be ignored). For example, the diameter of the objective lens of a telescope is only 20mm, which is about 2 centimeters. But the parameters marked are similar to 980x30, 20x50 or even larger, so it must be a false magnification.

Another parameter, which is a parameter like 131M/1000M, represents the field of view of the telescope. The principle is relatively complicated. There is a special article to introduce it. Here are the common field of view of telescopes from different manufacturers. The products may be slightly different, but the changes are not big. If you see exaggerated parameters such as 9999M/10000M printed on a certain telescope, then it must be a work of a (small private workshop).

Corresponding field of view angles of common telescope models (this parameter is for reference only, there may be slight differences between different manufacturers):

8x21 131m/1000m

10x25 96m/ 1000m

12x25 80m/1000m

7x35 147m/1000m

7x50 147m/1000m

10x50 122m/1000m

3. Whether the appearance is beautiful and fine, whether the structural design is reasonable, whether the rotating parts of the mechanism are flexible and comfortable, and whether the assembly quality (especially the focusing of the optical axis) is acceptable.

Regular telescopes have very high requirements for appearance when they leave the factory, and the factors that affect the appearance are controlled in all aspects of raw materials and assembly. When purchasing a telescope, you should pay attention to whether the appearance is beautiful and fine, such as leather decoration. Whether it is smooth and neatly trimmed (artisan works generally use low-quality decorative leather, and often use manual trimming methods. Due to the limitations of workers' technical level and equipment, the decorative leather has shortcomings such as unevenness and unevenness), and whether there is damping on the outer surface of the telescope. Grease residue and leakage. On this basis, we must also pay attention to whether the structural design is reasonable, such as whether the position of the focusing handwheel is reasonable, whether the hand feel is flexible, smooth, and comfortable, and whether the diopter compensation of the eyepiece part (usually the right eyepiece) rotates flexibly. .

Another point that requires special attention is whether the optical axis adjustment of the telescope is accurate. The parallelism of the optical axis of the left and right barrels of a regular telescope is calibrated to a certain angle using special instruments before leaving the factory (divergence ≤ 35 ', convergence ≤ 60'), when the parallelism of the optical axis exceeds this range, it is called optical axis out of tolerance, and will be judged as a seriously substandard product in a regular factory. Telescopes with extremely poor optical axes will cause adverse reactions such as dizziness and eye pain when used, and long-term use can cause serious damage to vision. Therefore, the adjustment of the optical axis is very strictly controlled in regular factories. The workers responsible for the adjustment are also the best workers selected from the assembly workers. After a long period of special training, it takes a long time to adjust a telescope. On the one hand, anecdotal works are restricted by product quality (inferior components, assembly quality and other comprehensive factors may determine that it is difficult to adjust this type of telescope to the standard optical axis), and equipment constraints (the price of the comparator is relatively high, and due to low productivity, a large number of equipment), on the other hand, in order to increase production and reduce costs (because inferior telescopes will lose more than they gain if they are adjusted according to formal adjustment methods), lowering inspection standards and even subjective adjustment methods are often used (the author has seen a The underground factory uses a method where workers face a white wall for calibration and is not equipped with any instruments. Qualification is judged only based on the workers' subjective feelings of dizziness.) The quality of the products is extremely insecure.

4. Whether the optical components are genuine optical components

The telescope market is mixed, and the development of telescope materials in the market is also changing with each passing day. Before 2000, inferior telescope manufacturers basically still used scrap and inferior optics. The components were shoddy, and after 2001, new resin lenses appeared, with even lower costs (it is reported that 0.2 yuan/PCS, the price of normal eyepiece lenses, even the lowest price of the most common small-size DCF telescope is 4- 5 yuan/PCS), the optical performance is further reduced. As for the method of identifying optical components - prisms, due to the large size of telescope prisms, it is difficult to manufacture them with resin, so the shoddy method is basically adopted. It is also easier to identify. Turn the telescope upside down and look from the objective end to a bright and open place. If you find a black broken line inside (compared to a DCF telescope using a roof prism) or a black stain, then this means This telescope is assembled from scrap products. The black broken lines and black spots are actually broken ridges and broken spots in the prism. For lens identification, carefully observe the eyepiece of the telescope. If it is not light blue but white (actually colorless), it means that the eyepiece is not coated. Why is it not coated? Because it is pressed with plastic resin, it will be deformed or melted by the high temperature during the preheating stage of the coating material before it is placed in the coating machine. However, the eyepiece system of a general telescope has several lenses. Some commercial works use the outermost lens to contain optical components, and the inner lens uses a resin lens to hide the sky. hehe! The devil is one foot high, and the Tao is one foot high. It turns out that this kind of resin lens has an inherent disadvantage, that is, the image quality is not good, especially the chromatic aberration and distortion are extremely serious. You might as well pick up a telescope and look at rod-shaped objects in the distance, preferably light-colored ones, such as telephone poles. If you find wires The edge of the pole's image is covered with a rainbow-like coating, and the edge field of view of the telescope is very blurry, which means it is a fake.

5. Are the accessories complete?

Any retail optical telescope generally contains the following accessories: lanyard, lens cleaning cloth, desiccant, lens bag, and a packaging box.

If these basic configurations are not complete, it is likely that the manufacturer is cutting corners in order to reduce costs, especially for PCF telescopes. The products produced by the manufacturer are generally not equipped with color packaging boxes. There are also some unscrupulous vendors who, under the guise of giving away a backpack for 10 yuan, rip off customers and resell the original leather bag of the telescope to the customer.

5. Resist the temptation of low prices, choose products carefully, and pay attention to whether the performance is consistent with the instructions

In 1997, the lowest market price for an 8X21 DCF telescope was 300 yuan. above. The lowest price currently on the market can reach more than 10 yuan. Price war is a weapon that has been tried and tested many times. Some friends are often deceived by the low prices and black lies of unscrupulous vendors. Although the price was very cheap, I ended up buying a bunch of junk. For example, the various colorful "military telescopes" and "Russian telescopes" that are commonly seen on the market are generally priced from more than 200 yuan to 80 yuan by vendors. Are they really cheap? This type of product only sells for more than 20 yuan in the Yiwu wholesale market. The cost reduction ability of the shop has really been brought to its extreme. Even if the price of optical rough glass purchased is based on the kilogram, this price is not enough to purchase and process such a telescope optical rough glass. So how did this telescope come about? It's simple, plastic with a little window glass. Therefore, when purchasing telescopes, users must make careful judgments based on the above principles, pay attention to whether the performance of the product is consistent with the instructions, and do not listen too much to the one-sided words of small traders to avoid being deceived.

The author believes that as long as you grasp the above principles, you will be able to buy a satisfactory telescope under normal circumstances.

Specifications: 10x40 Field of view: 6°30' 1000m field of view: 114/1000m Exit pupil distance: 12mm Exit pupil diameter: 4mm Resolution: 4.7" Specifications: 10x40 Explain the magnification of the telescope The magnification or magnification is 10 times. The diameter of the telescope's objective lens is 40 mm. For a zoom telescope, it may be marked as: 10-40x60, then the magnification is continuously adjustable between 10-40 times and the aperture is 60 mm. Pay attention to identification: it is meaningless to have a magnification that is much larger than the aperture. Some inferior telescopes are marked as: 999x50, etc. It is a kind of deception. In addition, some telescopes are marked as: "10x40 times", which is also irregular and misleading. : 6°30' indicates the field of view of the telescope. The greater the magnification of the telescope, the smaller the field of view. 1000-meter field of view: 114/1000 meters is another way to express the field of view, which refers to what the telescope can see at a distance of 1000 meters. The width of the range, the greater the magnification of the telescope, the smaller this parameter is. The exit pupil distance: the optimal distance between the eye and the eyepiece when the 12 mm telescope is imaging on the retina is related to the magnification of the telescope. Generally speaking, the exit pupil of a telescope with a high magnification is. The distance is smaller. The exit pupil diameter is large enough to ensure that the telescope can be used when the user wears a gas mask or glasses. The exit pupil diameter is 4 mm. For example, the exit pupil diameter of this 10x40 telescope is 4 mm. . Of course, this is an ideal state. Some telescopes may not be able to achieve this theoretical value due to optical path design and cost. Resolution: 4.7" refers to the ability of the telescope to resolve the smallest details. Generally, it is related to factors such as the specifications of the telescope, materials and workmanship.