What is a telescope? This question might seem trivial yet behind this global word, we uncover two main varieties of tools to observe the significant objects of our starry sky. The reflector telescopes space composed of mirrors whereas the refractor telescopes are just made that lenses. They space a lot of differences in between both of these categories, in terms of performances, durability and especially optical quality.

You are watching: It is much easier to build large reflectors than large refractors.

Reflector telescopes

Principle the a reflector

The newton telescopes space the many widespread reflectors in the market since of their straightforward building procedure and your low cost. The irradiate coming from a star goes within the optical tube and also is very first reflected top top the major mirror, located at the extremity. This main mirror is the master piece the the reflector. It has to collect and also make the light beams converging towards the eyepiece holder, the aspect where we put our eyes. Here, that is vital to discover a means to do the light beams going the end of the tube. Therefore, a secondary mirror is installed next come the prior aperture that the telescope, enabling beams to be deviated on the next of the telescope, and so, to watch an image.

The asset of a reflector is its main mirror’s very big size. The larger the mirror is, the brighter the objects appear in the eyepiece. However, a big mirror might quickly emphasize the optical aberrations of the telescope.

Optical high quality of reflectors

Theoretically, gaining a perfect round dot of a star requires having a newtonian reflector made v a hyperbolic primary mirror. In fact, together a winter is reasonably expensive and telescopes manufacturers pick rather a parabolic mirror instead, far less complicated to build. However, a parabolic winter is facing a defect: the coma aberration i beg your pardon deforms and also elongates the star about the fields of view.

More often, the low-cost manufacturers do not usage nor a hyperbolic no a parabolic mirror yet a spherical mirror. With such a geometry, you will never manage to focus perfectly the image of a star v your reflector, because of spherical aberration ; a delicate instance considering the astronomy calls for to observe and also photograph faint and diffuse celestial objects.

Reflectors in practice

Reflector telescopes are mainly open telescopes, meaning that the mirrors space exposed come the air, humidity and dust. This is why they need to it is in manipulated through precision and attention. For example, a mirror commonly exposed come this harsh environment might be much less reflective in ~ years, or placed it in a various way, its capability to reflect light decreases. Come this point, the clean of the winter is highly recommended, paying extreme attention to the vulnerable optical parts while dismounting the telescope.

A key element no to be forgotten through a newtonian-like telescope is the need to collimate it. This procedure permits you to perfectly readjust the alignment the the telescope and must it is in done before each observation or astrophotography session. This have to be ideally carried out every time you observe or start an astrophotography session.

Finally, reflector telescopes are very first choice instruments when you want to collect the most light as possible. Yet the side results are that you will need to know in details the optical system and should not be shy as soon as you will need to modify or clean the mirrors, as pointed out above.

Pros & Cons



Large mirror = better light collecting capacityNo chromatic aberrations (colored fringes roughly stars)Relatively short costOptical quality regularly disappointingCollimation and also mirrors clean processesOpen pipe = high vulnerability to dust, humidity..etcBulky and also heavy
Refractor Telescopes

The rule of keplerian telescope is very similar to a monocular. The light goes with the former lens, vital element make the light beams

converging come the eyepiece holder, wherein we download an eyepiece or a camera.Because of your compactness and ligthness, refractor telescopes carry out not collect as lot light as reflector yet have a much more stable optical quality and also do no need any kind of adjustement from the user/observer.

Optical quality of the reflectors

They have the specificity to let us observing the starry sky with an amazing sharpness and also contrast. These attributes are really appreciated in astronomical observation and also astrophotography.Nonetheless, keep attention ~ above what type of refractor friend choose. The cheapest are made that a solitary lens which undergoes the light dispersion. Consequently, a star will not be a solitary color point anymore yet surrounded by fancy rings. This is what we contact chromatic aberrration.

Today, there are different manners to eliminate this optical defect together as including a 2nd lens to acquire a double telescope.

Stellina : a refractor inspired by astrophotographers

Most the amateur astrophotographers prefer a telescope who durability, compactness and also simplicity to use are much better than the amount of light collected. As such they select refractor telescopes quite than reflectors.

derekwadsworth.com has actually responded come this demand and built a refractor telescope indigenous scratch, helped by one of the most reknown metrology activities in France : AiryLab.

The optical style is a Lanthane ED Doublet, permitting come decrease dramatically chromatic aberration. A special treatment on the lenses has been applied in bespeak to choose only the wavelength the interest and also reject all ultraviolet and also infrared lights.

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All these optimizations lugged into this telescope room just included in a small, transportable and also entirely automatic refractor. Refractors are thus a reliable selection for stargazers who want a dependable, pratical and easy-to-use astronomical instrument.

Pros & Cons



Impressive contrast and sharpnessLight and transportableClosed tube = protection versus humidity and dustMaintenance and also cleaning practically nonexistentSmall diameter = much less light collectedChromatic aberrationsHigher price