Everything You Need To Know About Telescopes Before Making A Purchase
What is a Telescope?
A telescope is an instrument that magnifies distant objects for observation. They use curved mirrors or glass lenses to focus light from the sky at night. However, modern telescope use mirrors because they’re lighter and easier to smoothen than lenses.
Telescope lenses and mirrors are known as “optics.” Powerful telescopes use large lenses or mirrors to view far away objects and dim things. Unlike smaller lenses or mirrors, their large counterparts gather more light and other types of electromagnetic radiation.
The shape of the optics focuses the light for viewing when people look into telescopes. It takes a perfect optics shape to concentrate light. A perfect lens or mirror is free from scratches, spots or any other kind of flaw responsible for blurry or warped images difficult to view.
Making perfect optics is difficult, especially for lenses than mirrors. Telescopes use absorption, emission, refraction or electromagnetic radiation reflection to allow for observation of distant objects.
Refracting telescopes were the first known practical telescopes developed at the start of the 17th century in the Netherlands. They use glass lenses to magnify distant objects in astronomy or terrestrial applications.
Apart from increasing distant objects’ angular size, telescopes also increased their brightness. When mirrors or lenses focus light or any other type of electromagnetic radiation, images become visible for viewing, studying or photography.
Non-astronomical instruments such as spotting scopes, theodolites, binoculars, transits, monoculars, spyglasses and camera lenses can be used in astronomy just like optical telescopes.
Telescopes come in varying sizes and shapes, ranging from the Hubble Space Telescope weighing many tons to a small plastic tube toy going for $2 or less. Amateur telescopes built with a small 6-inch scope can magnify a piece of writing on a dime about 200 feet away.
Most telescopes are available either as refractor or reflector telescopes. Although the former use glass lenses, the latter use mirrors. However, all the telescope perform similar tasks in different ways.
How Telescopes Work
Why is it impossible to see distant objects with naked eyes? It’s because the object doesn’t take up so much space in the eye retina (screen). It doesn’t cover enough pixels in the retinal sensor to see the object.
However, telescopes collect more light from the distant objects to create a larger image. Any part of the image can be magnified for better view or study.
Refractor telescopes feature objective lenses while their reflector counterparts are built with primary mirrors to gather light from the distant objects in high quantity. They bring the image or light to focus or a point.
The bright light in focus is then magnified or spread out using an eyepiece lens to occupy a large section of the retina. A magnifying glass lens uses the same principle to spread out or magnify a small image on paper over the eye retina to make it appear big.
A telescope is built with a primary mirror or objective lens that works together with an eyepiece to magnify distant objects. The optics collect a lot of light to develop a bright image inside the instrument. A magnifying glass then enlarges the bright image to ensure it occupies lots of space in the eye retina.
The two major properties of a telescope is its ability to gather light and the level at which it can magnify the image. The diameter of the aperture, the mirror or lens, influences the ability of a telescope to gather light.
It means large telescopes with large apertures collect more light than their smaller counterparts. The light is brought to focus and the final image brighter than in telescopes with smaller apertures.
The ability of a telescope to enlarge or magnify an image is dependent on the types of lenses in use. Although the eyepiece is responsible for image magnification, telescopes are able to enlarge images using all kinds of eyepieces. Therefore, the aperture of a telescope is more critical than its ability to enlarge images or magnification power.
Types of Telescopes
Telescopes come in various sizes and shapes. They’re categorized based on what they’re designed to view (such as solar telescopes or space telescopes) and how they work. With the first telescope invented in the 17th century, people have been watching the stars for decades.
Telescope inventors were fascinated by what could be out there and the possibilities. Unlike traditional telescopes, modern variations see deeper into space, revealing distant stars and galaxies.
Optical telescopes allow users to view galaxies and planets with eyes pressed against the eyepiece. A good example is the dioptrics, also known as refracting telescopes.
1. Refractor Telescopes
Invented in 1608, Hans Lippershey, a Dutch from Middleburg, is the brain behind the refractor telescope. The instrument was first used in the military, and Galileo was the first astronomer to use it. The telescopes used a combination of concave and convex lenses.
Kepler enhanced the telescope design in 1611 to feature two convex lenses. The new design relayed upside-down images. Although improvements have been made to the glass and lenses in modern refractor telescopes, they mostly come in Kepler’s design (larger and heavier).
At the mention of the word “telescopes,” what comes to mind is a refractor telescope. A typical refractor has the following parts:
i) A long tube – usually made from plastic, metal or wood. The tube houses the lenses, ensuring they’re mounted at accurate distance from one lens to another. It also protects the lenses from moisture, dust and light capable of distorting the image.
ii) A glass convex lens (objective lens) – mounted at the front end, the lens collects light from the distant objects, refracting or bending it to a focus almost at the tube’s rear end along the optical tube. The light hits a prism, mirror or diagonal responsible for directing it to the eyepiece. The optical path is adjustable to properly focus the light stream and create a clear, sharp image.
iii) Another glass lens (the eyepiece) – it magnifies the image, bringing it to the eye or camera sensor for viewing. Unlike objective lenses, eyepieces have shorter focal lengths.
Refractor telescopes can either be achromatic or apochromatic. Achromatic refractors lenses without extensive correction experience chromatic aberration. This is a rainbow that encircle images viewed through refractor telescopes. Light breaks up into different rainbow colors, resulting in color streams hitting the eyepiece at different times. The resulting images are displayed with false colors.
The refractors are designed to use “coated” lenses to minimize the issue. The film used to coat glass lenses minimize the amount of light being reflected while allowing more to go through the lenses. Additional lenses are also used in some designs to prevent chromatic aberration.
On the other hand, apochromatic refractors use lenses made from other glass types such as fluorite or designs built to use more than one lens. The goal is to protect images from chromatic aberration. Unlike their achromatic counterparts, they’re more costly.
At low focal ratios, achromatic refractors (built to use two lenses) result in color aberration around bright distant objects such as the Moon. It can have a purple or blue edge, which isn’t a true reflection of the moon in reality. The telescopes feature light optical tubes atop being low cost.
However, apochromatic refractors use a specialized glass and an optional third lens to further minimize color breakage. This more true in designs with low focal ratios to produce truer object colors, making them ideal for astrophotography and other applications that demand high quality images.
Despite improved image quality, the telescopes feature heavier optical tubes and come at costly price tags. Refractor telescopes can view binary stars and details in various planets due to their high resolution.
However, the largest objective lenses that can be made for refractors measure 4 inches (10cm). Due to the aperture’s cost per unit, refractors are generally costly. They use large apertures and lenses and long tubes of high quality.
The limited nature of a refractor’s aperture makes it unideal for viewing blurry or faint, distant objects in the deep skies such as nebulae and galaxies. This is unlike the possibility with other telescope types.
A refracting telescope is easy to use. However, they’re large and heavy, making them less portability. When buying a telescope for amateur astronomers, this is an important factor to consider.
Unlike other types of telescopes, nothing obstructs the optical path in a refractor telescope. This means the front lens and the full aperture work together to collect light and direct it to the eyepiece.
Although images produced are upside down, there’s no left/right or up/down in space, meaning the telescopes are just perfect for astronomical use. However, binoculars and spotting scopes built for terrestrial use feature a prism to correct image positioning.
Advantages of Refractor Telescopes
Disadvantages of Refractor Telescopes
2. Reflector Telescopes
Isaac Newton invented reflector telescopes in 1680 to solve the issue of chromatic aberration in refractor telescopes. He introduced a curved primary mirror made from metal into the telescope design (at the back of the tube) to gather and reflect light to a focus. Unlike lenses, mirrors eliminate the issue of chromatic aberration.
Newton also introduced a small, flat secondary mirror fixed at 45 degrees along the primary mirror’s focal path to prevent light from being reflected back into the tube. Instead, the flat mirror deflected out the image via the tube’s side to the eyepiece. They’re also known as Newtonian telescopes.
It also ensures nothing gets in the way of light coming into the telescope from the distant object. The secondary mirror doesn’t block the image due to its small size.
Rich-field reflectors are designed with wide fields, short focal ratios and low power of magnification. The focal ratio affects an image’s brightness. Unlike telescopes with longer focal ratios, rich-field types have wide fields to enable bright, panoramic views distant objects in the deep skies such as comets, galaxies, nebulae and clusters of stars.
Dobsonian reflector telescopes feature alt-azimuth mounting and a basic tube. Made from fiberglass, plastic or plywood, the telescopes are easy to build and inexpensive to buy.
The apertures of these types of telescopes range from 6 to 7 inches (15 to 43 cm). They’re ideal for viewing distant objects deep into the skies due to their low costs and large apertures.
Reflector telescopes are easy and cost-effective to make. Apertures as large as 10 inches (25cm) or more can easily be designed and made. This is due to low cost per aperture unit. They have the capacity to collect lots of light to support the production of sharp, bright images of blurry objects in the deep skies.
As a result, the telescopes are ideal for astrophotography use. The mirror is often made from glass with an aluminum coating. Also known as catoptrics, the telescope has a lens system and a tube similar to those of a refracting telescope. Reflecting and refractor telescopes have some things in common and others that differ.
Reflecting telescopes are smaller and compact, making them more portable than refractors. The instruments are dismantled for transportation. However, the mirrors can easily get out of alignment.
Polished metal was used in early reflector telescopes, but modern instruments use a glass with an aluminum coating to make the surface highly reflective just like a mirror. The primary mirror can either be spherical or parabolic (mirrors larger than 100 mm).
Reflecting telescopes produce inverted images, making it unsuitable for terrestrial use during the day because some images may not be desirable. The secondary mirror obstructs some incoming light, meaning a refractor with a smaller aperture can collect more light than a reflector with an aperture of the same size.
However, Newtonians can be made with large mirrors. Unlike refractors, reflectors can be made in aperture sizes as large as 16 inches (400 mm). The telescopes also offer the lowest cost per unit of aperture in inches. They range from truss to solid tube designs for apertures larger than 14 inches for easy dismantling to support transportation.
Reflector telescopes also feature soft covers to control stray light. The simple design of the instruments make them ideal for beginners or novice enthusiasts.
Advantages of Reflecting Telescopes
Disadvantage of Reflecting Telescopes
3. Catadioptric Telescopes
Also known as compound telescopes, these are a hybrid of reflecting and refracting telescopes, offering the best of both types. The term catadioptric is borrowed from the word “catoptrics” for reflecting telescopes and “dioptrics” for refracting telescopes.
Bernhard Schmidt, a German astronomer, made the first telescope of this kind in 1930. It was named the Schmidt telescope. It featured a primary mirror at the back and a glass plate at the front to prevent spherical aberration.
However, it had no secondary mirror and eyepieces, hence was used for photography. The primary mirror focused light to a photographic film.
Later in the 1960s, the Schmidt-Cassegrain telescope was invented. Unlike earlier design, it featured a secondary mirror responsible for directing light to the eyepiece through a hole in the primary mirror. Today, this is the most popular type of telescope in the market.
D. Maksutov, a Russian astronomer, developed the second kind of compound telescope. However, A. Bouwers, a Dutch astronomer, is said to have developed a similar telescope earlier in 1941.
Although the Maksutov telescope resembles the Schmidt in design, it features a corrector lens that’s more spherical in shape. The Maksutov-Cassegrain telescope (MCT) and Schmidt-Cassegrain telescope (SCT) designs are also similar.
Although SCTs range in size from 4 inches (102 mm) to 16 inches (400 mm), MCTs run from 4 inches (102 mm) to 7 inches (180 mm) in size. Large SCTs are costly. Unlike SCTs, MCTs feature thicker (heavier) corrector plates, making it unfeasible to make them in large sizes.
Just like the Newtonian telescope, the two designs have some form of light obstruction that partially blocks light. However, they fold the path of light within the optical tube, enabling longer focal lengths in compact designs.
A diagonal can be used with both designs to produce correct up-down image positioning, reversed from left to right as in refractors. A correct image diagonal can also be used for daytime terrestrial use. The MCT and SCT designs correct aberrations and come in short lengths for easily transportation.
But, unlike reflecting telescopes, the two designs are more costly. They also present some cons of both refractor and reflector telescopes such as light obstruction and collimation. However, the level of these issues is lower than in the individual telescopes.
Unlike in other types of telescopes, the primary mirror is adjusted to improve focus. Although focusing an image isn’t easy, the telescopes are small, light and portable. Featuring both lenses and mirrors, the optical telescope is ideal for viewing planets and galaxies.
Amateur astronomers, ranging from advanced to beginner user, can use this type of telescope. The telescopes can be used with GoTo computerized mounts for auto tracking of celestial or distant objects. Unlike other types of telescopes that can also use the mount, they’re a perfect match due to the compact nature of Cassegrain telescopes.
Despite being costly, the telescopes are easy to use, portable, provide beautiful views of the skies at night and require low maintenance.
Compound telescopes are ideal for visual astronomy and astrophotography without spending too much on an apochromatic refractor telescope or opting for a less costly achromatic refractor or reflecting telescope.
4. Radio Telescopes
Radio telescopes were invented in the 1930s. They use radio waves to produce images of distant objects in the terrestrial world. All terrestrial objects produce radio waves.
Large antennas with huge dishes are used to read the waves. The telescopes encompass huge dishes with three spokes at the center. However, they’re not ideal for amateur astronomers.
5. Gamma-Ray and X-Ray Telescopes
Infrared telescopes, just like radio telescopes, use rays that objects such as supernovas, the suns, and stars give off to produce images. They were invented in the 1960s. The instruments enable astronomers to view deep space events such as black holes and supernovas.
Gamma-ray telescopes detect spatial gamma rays to enable observation of deep space events that can’t be seen with naked eyes. There’s no chance of the images being altered by pollution because the telescopes are used at extremely high elevations.
They vary based on intended user and use. Traveling astronomers opt for compact and portable telescopes of this type. However, they generally consider the type of lenses used in an instrument and retail price.
The terrestrial bodies to be viewed depend on the type of mirror and lens built into a telescope. Gamma-ray telescopes and x-ray telescopes aren’t ideal for public use.
Specification/ Parts of a Telescope
Telescopes have various parts or specifications (they’ve been discussed in details in the buying guide). They include:
Accessories improve the functionality of telescopes. They include peep sights, filters, dew caps and detectors.
Whereas some telescopes come with standard finders, they can be bought separately.
Designed for setup within an eyepiece’s barrel, filters restrict light wavelengths incoming to create an image. They’re available as plastic or glass pieces.
Colored filters improve planetary image contrast while light pollution filters allow for viewing across polluted skies.
Filters can do any of the following:
Dew caps shield the optics and interiors of the telescope from moisture. It covers a telescope’s front end, extending tube length. Moisture condenses inside the dew caps instead of the interiors of the tube. Some types get heated to prevent condensation.
Just like the eye, other detectors detect light. However, CCD devices or digital cameras, film cameras and conventional lens cameras are other detectors handy if there’s need to take photographs of images under observation.
Spectroscopes, devices for measuring light intensities and wavelengths from a terrestrial object can also be used as a telescope accessory. Another detector is the photometer, a device used to measure light intensity. The two devices are used to create scientific measurements using telescopes.
Other accessories include masks, carry cases, diagonals, wedges, and tube rings.
Various manufacturers worldwide produce high quality telescopes, binoculars and related accessories for both professional and hobbyist use. The following are top two brands in the stargazing market of telescopes:
1. Orion Telescope Manufacturer
Established in 1975, Orion has been manufacturing high quality telescopes and binoculars for its customers worldwide. The company prides in its dedication to producing high quality products of top value with exceptional customer care services. It also offers 100% satisfaction guarantee on all its telescopes.
The range of telescopes the company manufactures target intermediate, beginner and advanced users. For instance, Dobsonian telescopes are ideal for intermediate users while beginners have access to entry-level telescopes.
On the other hand, the most experienced users have access to advanced Cassegrain telescopes, including their accessories. The telescopes and binoculars from this brand are popular for their premium optics available at unbeatable prices.
The binoculars on offer include compact binoculars, astronomical binoculars, waterproof binoculars, sport and hunting binoculars, and birding binoculars.
Telescopes and astrophotography accessories are designed to ensure users enjoy stargazing without spending too much. Accessories such as Barlow lenses for power-boosting, moon filters and high-tech computerized mounts increase astronomer’s viewing experience. With the astrophotography camera, capturing the images of objects in view is easy.
The manufacturer also ensures each stargazing session is comfortable, convenient and purposeful with its range of observing gear, astronomy books, telescope covers and cases, star charts and red LED flashlights.
What’s more, it avails resources on astronomy and astrophotography with its virtual community of amateur astronomers worldwide with the aim of sharing passion and knowledge in the field.
Extensive information and tips on binoculars, telescopes and astrophotography is accessible from the company’s community center. Users are also able to share their astronomy events, images, articles and reviews with the brand to get featured on its website.
2. Celestron Telescope Manufacturer
Celestron is a leading manufacturer of telescopes, sports optics, microscopes and related accessories. The microscopes range from digital microscopes to biological microscopes while binoculars range from spotting scopes to solar observing scopes.
On the other hand, telescopes include solar observing, optical tubes, astronomy binoculars, mounts and tripods, astroimaging cameras and top accessories. Founded in 1960 as Valor Electronics by Tom Johnson, the company has been a leading manufacturer in the optics industry for over 50 years.
With the C-8 game-changer as its first product, the company has grown its product portfolio to include exciting items based on revolutionary technologies and unique innovations. The first GoTo computerized telescope was manufactured in 1987. The first battery-powered telescope, the Ultima 2000, was invented in 1996.
The hand held telescope, the SkyScout Revolution, was invented in 2006. The award-winning handheld device is an innovative personal planetarium built to identify constellations, planets and stars using GPS technology. It has also manufactured auto-aligning telescopes with WiFi capabilities, making it a leading go-to telescope brand for many astronomers.
Maintenance and Cleaning of Telescopes
Every telescope needs proper care and maintenance to last long. Ranging from telescope optics cleaning to wiping the instrument’s surface, the right care also ensures your stargazing instrument performs optimally.
Telescopes, just like any other device, can get dirty. Dirt settled on mirrors and lenses scatters light to be focused. The result is dark skies appearing less dark and bright terrestrial objects looking less clear. It’s important to know when to be concerned about optics getting dirty and when to take it easy.
When the telescope isn’t in use, keep the lens caps on. A plastic bag, shower cap or dish cloth can easily cover tube’s front if there’re no lens caps. Use a rubber band to hold the bag, cloth or cap in place. A plastic canister or cloth wad can easily protect the eyepiece holder; one of 35 mm easily fits a standard-sized focuser of 1 ¼ inches.
Cap eyepieces on both ends or keep them in small plastic containers for food storage or plastic bags. Primary and secondary mirrors in reflecting telescopes can face downwards during storage to prevent dust from settling on them. Affordable storage cases are durable enough to protect eyepieces during transportation or while in storage.
Don’t touch mirror or lens surfaces because the acids present in the oil skin produces can progressively attack their optical coatings. Clean fingerprints off binocular lenses as soon as possible (explained below).
Dirt has mild effect on the performance of telescopes. Even so, unlike a scratched mirror, a dirty one can easily be cleaned. If done wrongly, cleaning optics can introduce sleeks or scratches on the surfaces. Therefore, cleaning shouldn’t be done regularly to minimize sleeks on the optics surfaces.
But, if the telescope must be cleaned, do it properly. Clean them once a year and keep fingerprints, and a mix of weak acids and fats from the optics surfaces. There’s no need to wipe the surfaces as soon as they get dusty.
However, remove pollen and fingerprints quickly to prevent alteration of the optics coating. Using filters with narrow bands for solar observations also require care. The lenses must be kept free from thick or heavy buildup of dust. Aggressive cleaning can also damage telescope optics.
Unlike a thick layer of dust on the surfaces, scratches can cause more damage to image contrast. Many scratches on the objective lenses can cause them to work like a grating, leading to errors. However, dust only causes transmission losses.
How to Clean the Eyepieces, Barlow Lenses, Filters, Correctors, Reducers, etc.
The eye lens is the only hardy part of a telescope, followed by the star-diagonal optical system. Don’t apply cleaning fluids directly onto the mounted optics surface lenses of refractor or reflected lenses.
It can easily soak via the cells of the lenses, relaying diet into the optics. It can also harm sealing rings and cause stains. The stains can only be removed after disassembling the telescope unit.
The lenses collimation can easily be removed. Clean the eyepiece lenses regularly to eliminate fingerprints and bodily fats that can heat up to receive an authentic hard coating. Unlike large objective lenses, technicians can use heat on lenses through hard processing of applying coating to prevent breakages.
High quality eyepieces such as acrylic lenses have hard surface coatings that can withstand regular cleaning without the risk of damage. Gently rub glass lenses using a soft cloth and gentle cleaning solution to eliminate residues. Dab the solution for cleaning onto the cotton wool or cleaning fabric instead of the eyepiece.
Clean hard coated filters just like eyepieces. Don’t use fluids on the lens surface facing the telescope. Instead of a cleaning cloth, camel hair or a soft brush can clean coma correctors, reducers, flatteners and other elements inside the telescopes. Protect them from fingerprints and pollens.
However, they aren’t hard-coated and thus require the same kind of care as refracting telescope lenses.
Cleaning Objective Lenses
It takes time and peace of mind to clean objective lenses. Refracting terrestrials also require cleaning. Avoid damaging the optics’ surfaces while cleaning. Pressurized air can also be used to remove dirt. Swipe or clean the optics from the center outwards to eliminate all stains.
Clean the mirrors only when dirty. Poor cleaning techniques can introduce scratches, which are more harmful than dust. Dismantle mirrors for cleaning and collimate or align them. Use a bag bellow to blow out dust instead of a can with pressurized air.
Soak the mirror to remove stubborn stains and use a soft brush to remove dust. Use moistened tissues dubbed with a cleaning fluid to dry the mirrors. This prevents surface scratching.
The best cleaning solution doesn’t leave behind smell, color, residue or striae that bacteria and fungi thrive on. They can feed on an entire coating. Distilled water is the best cleaning solution for rinsing the mirrors.
Protect the inside of telescope lenses, eyepieces, corrector plates and mirrors from moisture and condensation when replacing accessories. Protect optic from fingerprints and clean surfaces less often.
Only use soft cloths for cleaning and a fat free brush prior to cleaning using recommended solutions. Make sure that dust, and blows or shocks don’t get to the telescope.
Don’t use telescopes in the rain and avoid dusty places. Use dust caps to cover eyepieces and lenses. Dew can dampen telescopes. Moving a telescope indoors from outside can also moisten it.
Telescopes come in different sizes, shapes, weights and specifications. They’re also manufactured by different brands to meet varying application needs. Therefore, choosing the right stargazing instrument can be a nightmare.
Check out the buying guide below to help you pick the best digital telescope, solar telescope, telescopes for kids or hand held telescope as you deem fit.