Zoom lens (Barlow or Barlow lens): The focal length of the objective lens can be extended by two times (2X) or three times (3X) or more. The combined magnification of the telescope after using the zoom lens is the focal length of the objective lens ÷ the focal length of the eyepiece x the multiple of the zoom lens.
Extended data:
Telescope purchase skills:
1, optical quality and optical appearance are often contradictory. If you want both, you need to increase the budget greatly.
2. Every kind of telescope has a specific environment suitable for its use, so as to achieve perfect results. No telescope can do everything.
3. The volume of the roof prism telescope is the smallest in the same size, but the optical quality is often not as good as that of the Polo prism telescope.
4. The price of telescope depends on many external factors such as cost, profit and marketing strategy, and has little to do with the multiple of telescope.
5. The imaging effect of telescope depends on many factors, and the multiple is only one of them. It is not advisable to blindly pursue multiples.
Baidu encyclopedia-telescope parameters