Traditional Culture Encyclopedia - Photography and portraiture - What is a bull telescope?

What is a bull telescope?

Newtonian reflecting telescope

Advantages:

Since the cost of the reflector is much lower than that of the lens, for large-aperture telescopes, it is often used Reflective instead of bulky refractive. A portable designed reflecting telescope, although the lens barrel is only 500mm, the focal length can reach 1000mm. The focal ratio of Newtonian reflectors can reach f/4 to f/8, which is very suitable for observing faint extragalactic galaxies and nebulae. Sometimes it is also suitable to use this kind of telescope to observe the moon and planets. If you want to take pictures, a Newtonian telescope is great. But it is a little more troublesome to use than a catadioptric telescope. The Newtonian structure can concentrate light very well and obtain a very bright image at the focus.

Disadvantages:

The open lens tube allows air to circulate, which will not only affect the stability of the image, but also some dust will enter the lens tube with the flowing air and adhere to it. On the objective lens, if things go on like this, the coating on the surface of the objective lens will be damaged and its reflectivity will decrease. Since the objective lens of this structure is easy to break, you need to be careful when using it. For off-axis light, Newtonian telescopes produce coma. Telescopes with this structure are not suitable for observing terrestrial landscapes. Usually Newtonian telescopes have larger aperture and volume, so they are more expensive. Due to the addition of a secondary plane reflector, some light will be lost.