Telescopes have different designs and prices according to design requirements, selected materials, and lens quality.
Notes
Use of the telescope
:
When purchasing a telescope, you should first consider the environment in which it will be used telescope? What outdoor activities will it be used for.
Size and Weight:
If you need to carry the telescope for a long time, the lightweight style is a good choice.
The user’s eye distance:
General telescopes have devices that can adjust the eye distance to facilitate users to see things through the telescope, but wearing glasses is more or less Inconvenient; therefore, it is better to choose a soft rubber ring that can be folded on the eyepiece, which can adjust the correct eye distance and make the vision clearer.
Do you need waterproofing?
If your outdoor activities will be near water, require long vertical walks, or the weather will change, it is best to choose a telescope that is waterproof and nitrogen-filled. General telescopes are designed to be used during the day, so the larger the exit pupil of the telescope, the clearer what can be seen, and the more suitable for poor light conditions.
The optical quality of the lens is directly proportional to the price, so don’t buy the so-called customs confiscated goods on the roadside for the sake of petty and cheap. The quality is not good and there is no guarantee!
Meaning of the data
7×42 is marked on the telescope:
“7x” refers to the magnification of the telescope, which means that the telescope is passed through The observed object is seven times larger than when viewed with the naked eye. “42” refers to the aperture (diameter) of the telescope in centimeters. In the case of poor light, the larger the diameter of the lens, the more light sources can enter, and the clearer look. Hand-held telescopes are usually between 7x and 10x. A telescope of the same caliber, a model with a lower magnification has less image shake when hand-held, and usually has a wider field of view. A model with a higher magnification has a larger scene, but the background of the starry sky will look a little darker due to the smaller field of view.
Prism system:
Prism system is divided into two categories; one is porro prism and the other is roof prism. The Roof prism system is designed to be lightweight, small in size and light in weight, and is generally loved by outdoor enthusiasts. The Porro prism system, which allows more light sources to enter, is larger and heavier. Activities like boating that consider the brightness of the telescope more than the weight are quite suitable.
Glass quality:
The quality grades of telescope lenses are divided into Bak-4[ barium crown glass ] and Bk-7[ borosilicate glass ] borosilicate glass] two kinds. The Bk-7 is of standard quality, it costs less to manufacture, and it’s not too expensive. Bak-4 lenses are very clear and transparent, and the manufacturing process is complex and time-consuming, and is the best grade. The price is higher.
Anti reflection coating:
About 5% of the light is reflected when it enters the glass from the air or from the glass into the air. The objective lens, prism and eyepiece of each lens of the binoculars are added together, and generally there are 10 to 16 optical surfaces in contact with the air. If these optical surfaces are left untreated, approximately 50% of the total incident light is lost due to reflection.
Direct light can destroy the image presented in the telescope. In order to enhance the visual image, lenses and prisms need to be coated with a polarizing film. SILVA uses the patented EMERALD FIRE coating system to eliminate 99.6 % of harmful UV rays and IR rays.
Under normal circumstances, the single-layer antireflection coating design of the visual telescope has the best antireflection effect on the yellow-green light with a wavelength of 5500 angstroms, because the human eye is most sensitive to this wavelength of light. Therefore, it reflects more blue-red light, so we see that the lenses coated with a single-layer film are often blue-violet or red (that is, the so-called red-eye telescopes available in the market). Multi-coated lenses have a tinge of green or dark purple, like the coatings on camera lenses. A single-layer film that is too thickly plated will look green, and some unscrupulous manufacturers use it as a multi-layer film, so be careful when purchasing.
Binoculars are marked with a lens coating to indicate the optical quality of the binoculars. The types of its coatings are as follows:
Coated Optics (coating): It is a low-level anti-reflection coating. It only means that at least one optical surface is coated with a single layer of anti-reflection coating, usually on the outer surfaces of the two objective lenses and eyepieces, while the inner lenses and prisms are not coated.
Fully Coated: All lenses and prisms are single-coated, but if an optical plastic lens is used in the eyepiece, the plastic lens may not be coated.
Multi-Coated: At least one optical surface is coated with a multi-layer anti-reflection coating, the other optical surfaces may be single-coated or uncoated at all; usually only on two The outer surface of each objective lens and eyepiece is coated with multi-layer film.
Fully Multi-Coated: All lenses and prisms are AR-coated, some manufacturers are multi-coated on all optical surfaces, “while others Only part of the optical surface is coated with multi-layer film, and other surfaces are still coated with single-layer film.??
Exit pupil: Exit pupil refers to the aperture measuring device that allows light to enter the eye. The larger the Exit pupil, the brighter the image will be, especially in the early morning, dusk or in the shadows, it is most effective.
Field of view: The field of view is expressed in a range of 1~1000 meters. The larger the telescope, the smaller the field of view. Larger telescopes usually require a stand to hold it steady.
Eye relief: Eye relief is the furthest distance the eye is from the surface of the eyepiece when we can see the full field of view in the binoculars. For clear images, the eye distance must be correct. If you wear glasses, you must choose a soft rubber ring attached to the eyepiece that can be flattened or folded; so that the distance between the eye and the eyepiece is not offset by wearing the glasses. If you use binoculars with a short viewing distance (such as 8mm) to view the scene, in addition to the eyepieces that are easily stained with the grease on the eyelashes, because the eyes must be very close to the eyepieces to see all the fields of vision clearly, long-term viewing will also cause a sense of oppression, making people feel uncomfortable.