A reflector telescope or reflecting telescope has a concave mirror that gathers light from the object. Its most common form is the Newtonian reflector (invented by Isaac Newton), with a concave (dish-shaped) primary mirror in the bottom end of the telescope. A small diagonal secondary mirror placed near the top of the telescope reflects the light coming from the primary mirror to the side of the tube, where the observer see the astronomical objects through the eyepiece. The design of this telescope allows astronomers to see things way out in space that don’t emit much light. Almost all of the major telescopes used in astronomy research are reflectors.
Since all wavelengths reflected off the mirror in the same manner reflector telescopes lessen the worries of chromatic aberration. These scopes are more fragile and require more maintenance than the others. An open optical tube design allows image-degrading air currents and air contaminants, which over time will degrade the mirror coatings and decrease performance. The optical components can go out of alignment, requiring collimating.
These simple designs are highly popular among amateur astronomers worldwide. Newtonian reflectors are great telescopes, available with good aperture size at reasonable price. They work for deep sky as well as planetary viewing. Of course you will be able to see more with the larger aperture. Especially in a reasonably dark sky, you get excellent images of fainter clusters, galaxies and nebulas. Their large apertures allow them to serve up fine, highly-resolved images of planets and deep-sky objects alike. These scopes are unsuitable for terrestrial (earthly) viewing as they produce an upside-down image and are designed exclusively for astronomy. Reflecting telescopes come in many designs and variations and often use extra optical elements to improve image quality or to help with the placement of the image which makes it easier to be seen. As reflecting telescopes use mirrors to focus light, and since they are cheaper they can be made much larger. All major astronomical telescopes built now are reflectors. The largest optical telescopes are currently the Keck telescopes that have 10 meter mirrors and the brand new Gemini telescope that have 8 meter mirrors.
There are several advantages associated with reflecting telescopes:
- Easy to use and to construct.
- Great for faint deep sky objects such as remote galaxies, nebulae, and star clusters because of their larger apertures for light gathering.
- Low in optical irregularities and delivers very bright images.
- Reasonably compact and portable.
- A reflector costs less compared to refractors and catadioptrics since mirrors can be manufactured at less cost than lenses.
There are several disadvantages of reflector telescope:
- Not usually suited for terrestrial applications.
- Mirrors cause some slight light loss when compared to the lenses of a refractor telescope.
- It has an open design which means that more dust can penetrate the mirrors and lead to more cleaning.
- Reflectors require a little more maintenance and care than refractor telescopes.
Reflecting telescopes are best suited for amateur, children, beginners and for those who are pursuing a professional level in astronomy, despite all its disadvantages.