Refractor Telescope is the lens of the telescope. Divided into two types: the concave lens as the eyepiece called Galilean telescope; the lenticular lens as the eyepiece called the Kepler telescope
The Galilean telescope is a telescope with an objective lens that is convex and an eyepiece is a concave lens. The real image of the light refracted by the objective is focused on the back of the eyepiece (behind the person's purpose), which is like a virtual image of the eyepiece, so that it is refracted into an enlarged upright virtual image. Galileo telescope magnification is equal to the focal length of the objective lens and eyepiece focal length ratio. The advantage is that the lens barrel is short and can be just like, but its field of view is relatively small. The two magnification Galileo telescope side by side with a bolt button in the middle can simultaneously adjust the clarity of the device, known as the "opera mirror"; easy to carry, often used to watch the show and so on. Galileo invented the telescope in human understanding of nature's history occupies an important position. The advantage is that the structure is simple, can be directly into the image.
The Kepler telescope consists of two convex lenses. Since there is a real image between the two, the reticle can be conveniently installed, and all kinds of excellent performance, so the current military telescopes, small telescopes and other professional telescopes are using this structure. But this kind of structural imaging is upside down, so add a positive system in the middle.
Just as the system is divided into two categories: Prism imaging systems and lens imaging systems. Our common front and rear narrow binoculars have both double-sided prism systems. The advantage of this system is that the optical axis is folded twice as much as it is astigmatism, greatly reducing the size and weight of the telescope. Lens as system uses a complex set of lenses to reverse the image, the higher cost.
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