Telescope purchases with knowledgeable language professional commentary help you see more clearly and farther
Telescope purchases
Purchase according to the environment
Don’t forget to buy a waterproof binoculars if you are thinking of traveling by sea or on the coast.
If you want to go out for sightseeing, you can buy a small telescope
with zoom function.
If you plan to go hunting in dangerous areas that can be seen from a distance but not near, you should buy a high-power telescope.
For hunting or long-term When traveling abroad, it is best to buy a variable magnification telescope, and 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 low magnification and a large field of view for rough search. , and then take a closer look with a high power, small field of view.
What is the term for a telescope?
Aperture
This is the most important factor when choosing an astronomical telescope. The primary function of a telescope is to collect light, no matter how large the magnification is, the larger the aperture is to image The better. The aperture of the telescope refers to the glass diameter of the telescope objective or the size of the main lens, expressed in millimeters or inches. The larger the aperture, the stronger the ability to collect light, and the better the imaging. The larger the aperture, the better the image. The details of the picture will be clearer. For example: when observing a spherical nebula of M13, a 4-inch aperture telescope needs a 150 power supply, but an 8-inch aperture telescope also uses the same power supply, but the nebula The image is 16 times clearer than with a 4′. Even the stars in weak light can be seen clearly. Considering that the user needs an inexpensive and easy-to-carry telescope, choose a large-diameter telescope as much as possible. Large-diameter The pictures taken by the telescope have higher contrast, better resolution, and clearer. The Celeste telescope has ‘5-inch aperture’, ‘8-inch aperture’ and ’14-inch aperture’.
< strong>resolution
This involves the ‘Dawes limit’. To distinguish two closely spaced twin stars, the theoretical resolution of a telescope is 4.56 divided by the diameter of the telescope For example: a resolution with a diameter of 8 inches is 0.6 (4.56/8=0.6) The factor that directly affects the resolution of the telescope is the diameter of the telescope, so the larger the diameter of the telescope, the better the resolution. However, the resolution It also depends on the influence of the atmospheric air and how sharply people look at the object.
Exit Pupil Diameter
Exit Pupil Diameter is when the telescope does not need the eyepiece. A circular beam of , expressed in mm (millimeters). Calculate the diameter of the exit pupil, for example: a telescope with a diameter of 8 inches (203mm), use an eyepiece with a focal length of 20mm to magnify 102 times, and the diameter of the exit pupil is 2mm (203 /102 = 2mm). Or you can get the exit pupil diameter by dividing the focal ratio of the telescope by the focal length of the eyepiece.
Limiting Magnitude
Astronomers use a magnitude system to describe the class of bright stars , a star is considered to have a certain magnitude. The higher the level, the dimmer the star is. Each star has an increasing number (larger magnitude value), which is about 2.5 times the magnitude, using The faintest stars you can see with the naked eye are about 6th magnitude (when in the night sky), while the brightest stars are 0th magnitude stars (or even negative). The faintest star seen with a telescope (when all kinds of environments are the best) is the so-called limit star. The limit star directly depends on the aperture of the telescope. The larger the aperture, the higher the limit star seen. . The rough formula for calculating the limiting magnitude is: 7.5 + 5 LOG (caliber is expressed in cm). Example: The limiting magnitude for an 8′ telescope is 14.0 (7.5 + 5 LOG 20.32 = 7.5 + (5×1.3) = 14.0). The conditions of the atmosphere and the visual acuity of the observer will have an effect on the limiting magnitude. The photographic limit magnitude is about two or more higher than the visual limit magnitude.
Field of View
The range you can see when looking at the sky through a telescope is the field of view, which is expressed in terms of the angle of an arc. The larger the field of view, the larger the scope of observation you can see. The formula for calculating the field of view angle is the index obtained by dividing the field of view angle of the eyepiece used by the magnification of the telescope. For example: if you are using an eyepiece with a field of view of 50 degrees, and you are using a telescope plus eyepiece with a magnification of 100x, then the field of view of the telescope is 0.5 degrees (50/100 = 0.5). Manufacturers usually specify the field of view of their eyepieces. Generally speaking, the larger the field of view, the larger the field of view, and the more you can see when observing the starry sky. , using a low-power astronomical telescope to see a wider field of view than using a high-power telescope.