Choosing a telescope is a very confusing thing. When we buy a telescope, we are dazzled by the overwhelming publicity in the store or on the Internet. However, we are at a loss due to the lack of telescope knowledge, so we search for the knowledge on the Internet at random, and finally get confused and even misled.  Some businesses take advantage of this to produce inferior fake products, shanzhai products, shoddy goods, profiteering.  So we’re kind of in two minds about how do you judge a telescope, so let me share with you some personal experiences.  

How do you judge a telescope?  

A telescope can be evaluated in the following ways.  

1. The depth of field  

For bird-watchers, depth of field is a relatively contradictory parameter. If the depth of field is large, it does not need frequent focusing and is convenient to use. However, for observing forest birds, foreground and background are not easily blurred and birds are not easy to stand out.  While the depth of field is small, although the foreground and background are blurred obviously when observing forest birds, and the theme of birds is prominent, it is necessary to re-focus once the distance changes, and fingers should always be placed on the focusing wheel, which is quite tiring.  It depends on personal preference, there is no fixed standard.  

2. The sealing  

Far often undertake outdoors, observe environment changeability, had better choose can prevent soak water (water pressure waterproof) telescope, such ability makes mirror interior maintains seal and stability, do not have fog, not long mildew.  

3. The comfort  

Comfort varies from person to person.  Generally speaking, the surface coated telescope, not only has good shock resistance but is also more comfortable to hold.  The weight of the mirror determines whether it is easy to use and carry for a long time.  Usually, people choose telescopes that are more durable.  

4. The focal length  

The focal length of a telescope mainly refers to the focal length of the objective lens.  The telescope optical system usually consists of two systems of finite focal length, in which the image square focus of the first system (objective lens) coincides with the object square focus of the second system (eyepiece).  For the same object, the longer the focal length, the larger the image of the object in the negative.  

5. The lens  

A good telescope must have a good lens, the lens is the soul of the telescope.  The general judgment is very simple.  Open the lens cap and objective cap and look down through the eyepiece. If it looks like the center lens is more and more round, it will feel like there is no lens at all, the better.  Second, dropping a few drops of water onto the eyepiece and hitting the lens of the telescope is like sliding water on a lotus leaf without leaving a trace.  The above two points show that the lens is smooth after many multi-layer coating is assured of a high-quality mirror.  

6. Telescope coating  

The coating is to increase light transmittance, reduce reflection and make the imaging color more reductive.  Without the coating, the image you see is either a little grayish-black or the green may turn yellowish-green.  Therefore, it is necessary to choose a multi-layer coating, and it is FMC full-surface broadband coating with multi-layer coating on all lens surfaces.  

7. Caliber  

Larger telescopes tend to produce better observations, but they also cost more.  The larger the volume, the heavier the weight, the smaller the diameter, the observation effect is almost, but the small size, lightweight and easy to carry.  General hand-held choose 20-50 mm caliber of the double barrel, if the tripod, the caliber can choose 50-100 mm.  

When you are buying a telescope to judge the quality of the telescope can refer to the above points, remember not to blindly cheap, otherwise it will only outweigh the gain.