Principle and Applications of Telescopes: Refracting, Reflecting

and Catadioptric Telescopes

Xinyue Hu

Suzhou High School IB Programm, Suzhou, China

Keywords: Refractor Telescope, Reflecting Telescope, Catadioptric Telescope, JWST.

Abstract: As a matter of fact, telescopes play the most vital role in astrophysics and cosmology observations, which are

the key facilities for recording the spectrum as well as intensity information. In recent years, thousands large

telescopes have been built and some amazing observations have been achieved based on the advanced

telescopes (e.g., black holes recording from EHT and galaxy formation by JWST). With this in mind, the

passage mainly introduces three types of frequently used telescope, i.e., refractor, reflecting, and catadioptric

telescopes. At the same time, their recent developing results in astronomy fields such as discoveries of

extraterrestrial as well as blackbody are discussed. The consisting of the facilities as well as the detection

parameters and categories are also summarized and evaluated. According to the analysis, their limitations

such as the change in atmosphere directions and prospect in the future are clarified and demonstrated. Overall,

these results pave a path for further investigation of telescopes and cosmology observations.

1 INTRODUCTION

A telescope improves eyesight by magnifying far-off

objects and making them seem closer to the observer

(Ryan, 2024; Taylor, 2004). Mostly used in

astronomy to let people explore the universe, the

telescope is a priceless and indispensable scientific

tool. A telescope is a device used to gather visible

light or at different wavelengths emitted radiation.

Big telescopes can catch far lighter than the human

eye can, much as a garbage can hold onto more

rainfall than a coffee cup. Scientists today are unsure

of exactly who the first individual to design the

telescope was. Still, historical records show that a

Dutch sight producer openly announced in the

seventeenth century the creation of a new optical tool

allowing amplification of far-off objects. This is the

first known account of the telescope's invention.

Still, Galileo Galilei is recognized as having

greatly advanced astronomical telescope use. After

erecting his own telescope in 1609, Galileo produced

some significant discoveries including lunar surface

research, identification of Jupiter's moons, and

viewing of Venus's phases. These findings validated

Copernicus's heliocentric view and disproved the

geocentric model of the universe. Telescope

technology developed still throughout the next

centuries. It was very amazing how Isaac Newton

invented the reflecting telescope in 1668. By means

of mirrors rather of lenses, Newton's discovery

eliminated chromatic aberration and made it possible

to build larger telescopes. Development of big

refracting telescopes made considerable advancement

in the 19th century (Mountain & Gillett, 1998).

Among such well-known examples are the 40-inch

telescope at Yerkes Observatory, considered as the

largest refractor ever constructed. The 20th century

brought fresh ideas and more successes. Radio

telescopes provide the vision of astronomical objects

radiologically active. Several amazing discoveries

made possible by this scientific development were the

identification of cosmic microwave background

radiation and pulsars.

Space observatories have reached incredible

resolution by avoiding air distortion—that of the

Hubble Space Telescope launched in 1990. The

Hubble telescope reveals among the most important

facts the fast expansion of the universe. One of the

most far-off galaxies yet discovered, JADES-GS-

z14-0 has been located and studied using the James

Webb Space Telescope (JWST). This galaxy, 13.4

billion light-years distant, lived at the era of just 350

million years old for the universe. This outcome

describes the conditions of the universe just following

the Big Bang and the initial phases of galaxy

Hu, X.

Principle and Applications of Telescopes: Refracting, Reﬂecting and Catadioptric Telescopes.

DOI: 10.5220/0013075500004601

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Innovations in Applied Mathematics, Physics and Astronomy (IAMPA 2024), pages 307-312

ISBN: 978-989-758-722-1

307

development. One significant discovery is about GN-

z11, a young galaxy surviving 430 million years after

the Big Bang. Notable discovery made by James

Webb Space Telescope (JWST) researchers is that

this galaxy harbours a supermassive black hole

presently accreting matter. GN-z11 is the galaxy

currently possessing the furthest known black hole

distance. This outcome offers important new insights

on the evolution of black holes in the early universe.

Moreover, exposed by JWST spectroscopic data are

ionized chemical constituents of GN-z11 (Bunker et

al., 2023)

This outcome suggests that, even in the early

periods, intricate processes involving elements with

high atomic numbers were happening, which is

crucial to grasp the chemical backdrop of galaxies.

The results reveal how well JWST can probe far-off

areas of the cosmos and offer unparalleled insight into

the early universe, therefore advancing the

knowledge of black hole development, galaxy

creation, and the evolution of the universe.

2 GOALS AND FRAMEWORK

FOR STATE-OF-ART

FACILITIES

From Galileo's day, telescopes have been absolutely

vital in helping to grasp the universe. telescopic

technology is driven ahead by the search to

comprehend the universe and therefore learn more.

Appreciating the relevance of telescopes in the

evolution of science and technology calls for a

complete awareness of the basic principles and

practical uses of them. The potential of telescopes to

increase human vision beyond the boundaries of

natural eyesight drives most of the research on their

ideas and applications. By means of far-off celestial

object analysis, telescopes expose the secrets of

planets, stars, galaxies, and other cosmic happenings.

Analyzing the universe satisfies the innate curiosity

and clarifies basic issues like its evolution,

composition, and genesis.

In addition, numerous useful applications call for

telescopes. Fundamental tools for black hole research,

exoplanet finding, and cosmic microwave

background radiation study in astronomy are

telescopes. Essential instruments for tracking weather

patterns, viewing and evaluating environmental

changes, and maintaining national security by means

of remote sensing and surveillance are telescopes. If

one is to make good use of telescopes in both

theoretical and practical environments, one must have

a firm awareness of the fundamental notions of

optical design, light collecting, and resolution. Since

it presents potential for new discoveries, the study of

telescopes is essential and fascinating as technology

progresses.

The essay consists in three main parts: principles

of telescopes, applications in astronomy, and

applications in other fields. It reviews basic ideas in

telescopes as well as useful applications. Reflectors

and refractors are two main types of telescopes; taken

together, they account for six basic shapes. In charge

of light collection, the objective tells exactly the kind

of telescope to be utilized. The main objective of a

refractor telescope is formed by a glass lens. The light

bends as it passes the glass lens at front of the

telescope. A reflector telescope's main optical

component is a mirror. Strikes produce reflection of

light in the mirror facing the rear of the telescope. A

Catadioptric Telescope, which combines mirrors and

lenses, is another kind of telescope used to exploit the

benefits of both systems. Made expressly to fix

optical defects, these flexible devices produce high-

quality images with little chromatic and spherical

aberrations.

The first type of telescope this study will

introduce in this passage is catadioptric telescopes.

These optical instruments are designed especially to

obtain photographs of far-off objects. This approach

uses reflective optics—like mirrors—and refractive

optics—like lenses—to clearly integrate mirror and

lens optics, hence improving performance and

manufacturing process efficiency. Combining the

words "dioptric," which defines a system utilizing

lenses, with "catoptric," which specifies an optical

system using curved mirrors, produces the phrase

"catadioptric," a gadget that catches clean, high-

quality images suited for both direct viewing as well

as shooting astronomical objects. Professionals,

teachers, and amateur astronomers find these tools

particularly enticing since they mix the optical

benefits of the reflecting and refracting designs

(Bahrami & Goncharov, 2010).

Usually featuring apertures between 90 mm (3.5

inches) and 355 mm (14 inches), consumer-grade

devices Whereas Schmidt-Cosegrain telescopes

usually have focal lengths between 1000 mm and

3000 mm, Maksutov-Cassegrain telescopes usually

have standard ranges from 1000 mm to 2000 mm.

Although Maksutov-Cassegrain telescopes typically

have focal ratios between f/12 and f/15, Schmidt-

Cassegrain telescopes typically have focal ratios

between f/10 and f/2.3. Furthermore, catadioptric

telescopes are typically mounted equatorial or

altazimuth depending on whether they are used for

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visual observation or astrophotography. Smaller

models of consumer-grade catadioptric telescopes

can weigh few kg, whereas bigger aperture models

can weigh more than twenty kg. The weight of the

object determines its mobility and simplicity of setup

and transportation. The manufacturer and the specific

type of catadioptric telescope can affect the specified

exact values. Professional and observatory-grade

telescopes usually have longer focal lengths, larger

apertures, and more complex optical systems than

consumer-grade telescopes. Mostly employed for the

detection of gravitational waves is the catadioptric

telescope. Catadioptric telescopes help detect and

analyze gravitational waves even though they are not

directly visible with optical telescopes. Telescopes

are indispensable for multi-messenger astronomy by

means of electromagnetic emissions, such as those of

gamma-ray bursts or kilonovae since they enable

exact location identification of gravitational wave

occurrences. Additionally, this requires much effort

in public outreach and astrophotography.

Catadioptric telescopes are regularly used to capture

amazing images of celestial objects in public outreach

campaigns and amateur astronomy. These pictures

are meant to inspire and enlighten the people on the

beauties of space.

Second type telescopes, known as refractors,

collect more light than the human eye could detect.

Through concentration of light, they raise the

visibility, clarity, and size of far-off things. Usually

speaking, refracting telescopes have two main lenses.

Generally speaking, the larger lens is known as the

objective lens; the smaller lens used for seeing is

termed the eyepiece lens. The objective lens lets the

eyepiece lens operate as a magnifying glass, showing

a magnified version of the image generated by the

objective lens by generating a precise and small

image of the object. To enable more exact and clear

observation of far-off astronomical objects such stars,

planets, galaxies, and nebulae, a refractor telescope

gathers and concentrates light emitted by them.

Refractor telescopes mostly serve to view celestial

objects in the night sky. Usually made of glass,

refractor telescopes gather and concentrate light using

an objective lens to produce an image at the eyepikey

or camera sensor. The capacity to capture exact and

well-defined images of celestial objects is one benefit

these telescopes give aficioners and amateur

astronomers. Viewers may study the Moon's craters,

planets in the solar system, star clusters, nebulae, and

far-off galaxies. Reflector telescopes are often used in

astrophotography, the technique of photographing

astronomical objects by mounting cameras on

telescopes. For in-depth studies of planets, galaxies,

and nebulae, their ability to create clear, accurate

images with obvious brightness variances makes

them perfect (Onah & Ogudo, 2014).

Usually running from 50 mm (2 inches) to more

than 150 mm (6 inches), an amateur refractor

telescope has a focal length. Wider apertures catch

more light, resulting in crisper, more brilliant photos.

Usually ranging in focal lengths between 400 and

2000 mm, refractor telescopes may include even

larger spans. For close examination of minute details

in celestial objects, longer focal lengths produce

better magnification and narrower fields of view. The

degree of magnification might vary greatly depending

on the exact mix of the focal length of the eyepiece

being used with the focal length of the telescope. For

a telescope with a 1000 mm focal length and a 20 mm

eyepiece, for example, the magnification that results

will be 50x (obtained by dividing 1000 mm by 20

mm). Excellent contrast, reduced chromatic

aberration, and great optical accuracy define refractor

telescopes of top quality. Quality is affected by lens

grinding, coating technology, general design, and

degree of accuracy in all three. Reflector telescope

focal ratios usually fall between f/5 and f/15 or above.

In astrophotography, a telescope with a smaller f-

number—say, f/5—has faster exposure time and a

higher light-gathering capacity. The dimensions of

the telescope tube may change greatly based on the

aperture and focal length. Tubes can have lengths

between 500 mm and more 2000 mm and diameters

between a few inches and several inches. The exact

kind and intended use of a refractor telescope can

produce significant changes in its values. Usually

preferred by amateur astronomers are telescopes with

apertures between 70 and 120 mm and focal lengths

between 600 and 1200 mm. These decisions provide

excellent optical performance and portability,

therefore creating a nice balance. Longer focal

lengths and much wider apertures of professional-

grade reflector telescopes help to enable more exact

observations and photographs.

The most current update from January 2022 states

that refractor telescopes have been crucial for many

recent observations and discoveries. Reflector

telescopes have made it feasible in great part to find

exoplanets orbiting stars outside of the solar system.

Often included in these discoveries are exact

measurements of a star's brightness over a certain

period of time since they verify the presence of

planets in orbit. Reflectors have tremendously helped

to find and analyze supernovae, the violent death of

large stars. These facts help astronomers to better

understand the mechanics of explosions, the process

of star evolution, and the resulting debris. Moreover,

Principle and Applications of Telescopes: Refracting, Reﬂecting and Catadioptric Telescopes

309

refractor telescopes actively participate in large-scale

studies aiming at map the geographical distribution of

galaxies and galaxy clusters over the universe.

Surveys offer crucial data on the structure of the

cosmos, dark matter distribution, and galaxy

evolution across cosmic time.

The third type of telescope is the reflecting

telescope, utilizing the phenomenon of light

reflection (Mullaney, 2014). A far-off object's light

enters the telescope and interacts with the main

mirror—a large concave mirror at the rear of the

device. This mirror precisely reflects and focuses

light. Usually, a reflecting telescope uses a secondary

mirror to deflect light from the main mirror as it gets

near its point of convergence. The primary use of this

secondary mirror is to divert light toward an eyepiece

or camera. The eyepiece magnificuates the focussed

light, therefore providing the spectator with a crisper,

more detailed picture of the far-off object. The main

purposes of a reflecting telescope are to effectively

gather light from a far-off object and focus it precisely

to generate a detailed and clear image. Larger main

mirrors in telescopes help them to gather more light,

therefore enabling them to view objects fainter and

further away. Since the former allows the use of

bigger apertures and improves light gathering

capabilities, constructing gigantic mirrors is a more

sensible and affordable choice than making huge

lenses. Reflecting telescopes can be made in a range

of configurations including Newtonian, Cassegrain,

and Dobsonian to meet several observational needs.

The distance separating the main mirror's focus

point from each other. The ratio of the focal length to

the aperture decides the field of vision and the

telescope's light collecting capability. An auxiliary

mirror helps to focus light from the main mirror

toward the eyepiece or camera. The James Webb

Space Telescope (JWST) has been able to throw light

on the early phases of the cosmos by effectively

photographing galaxies that developed soon

following the Big Bang (Rigby et al., 2023). The

telescope also now searches for elements like water

vapor and studies extraterrestrial atmospheres. This

study helps to better grasp the possibilities of

extraterrestrial life. A sketch of JWST is presented in

Fig. 1 (Greenhouse, 2016).

The Event Horizon Telescope (EHT), a

worldwide network of radio telescopes running as a

single telescope with Earth-sized proportions, has

achieved a major milestone. Released in April 2019

by the EHT project, the first-ever picture of a black

hole at the core of the M87 galaxy This amazing

achievement has confirmed Einstein's general theory

of relativity and yielded unequivocal, visible

evidence of black holes (Gold et al. 2020;

Ramakrishnan et al., 2022). Restraints and

Prospectives, A sketch for the facility is shown in Fig.

2 (Event Horizon Telescope Collaboration. 2019).

Figure 1: A sketch of JWST (Greenhouse, 2016).

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310

Figure 2: A sketch of EHT (Event Horizon Telescope Collaboration. 2019).

3 LIMITATIONS AND

PROSPECTS

Because the atmosphere of the Earth can change the

direction of arriving light, images can get distorted.

Sometimes known as air turbulence, this phenomenon

limits the degree of detail ground-based telescopes

can gather. Furthermore, adaptive optics systems can

minimize some air distortion; yet, their efficiency

relies on the wavelength and their complex

construction. Furthermore, providing better sharpness

and collecting more light are larger mirrors. They do,

however, also have the disadvantage of being more

substantial and challenging to build and strengthen

structurally.

As the JWST shows, the application of mitigating

measures entails the combination of lightweight

materials with cutting-edge technologies, such

segmented mirrors. Still, engineers still find great

challenges from these components' weight and bulk.

Operating outside the atmosphere of Earth, the James

Webb Space Telescope and the Hubble Space

Telescope stop light pollution and atmospheric

distortion. Future satellite telescopes will be able to

record even higher degrees of detail and resolution.

Starting in the middle of the 2020s, the Nancy Grace

Roman Space Telescope will look at dark energy and

problems associated to exoplanets. Ground-based

telescopes will be able to more precisely lower

atmospheric turbulence and approach space

telescopes in terms of image clarity as adaptive optics

technology develops. Modern adaptive optics

technology will enable the Extremely Large

Telescope (ELT) under construction in Chile to reach

unheard-of clarity. Using segmented mirrors makes

larger main mirrors that would not be feasible to build

as a single piece possible. This method allows one to

build larger and more sophisticated telescopes. The

seven 8.4-meter Giant Magellan Telescope (GMT)

components taken together have an aperture size of

24.5 meters. Reflecting telescopes point to a bright

future full of fascinating new discoveries right around

the horizon. These advances will keep expanding the

boundaries of the knowledge about the universe.

4 CONCLUSIONS

To sum up, telescopes have profoundly transformed

the comprehension of the cosmos, each with benefits

and challenges, the understanding of the universe has

changed significantly. Simple and robust devices

using lenses, refracting telescopes are well-known.

They are vulnerable to chromatic aberration, though,

and have restrictions in size. Because of their mirror-

based architecture, which also enables excellent

resolution free from chromatic aberration, reflecting

telescopes are better in gathering light. They must

nevertheless be kept more regularly. Catadioptric

telescopes mix lenses and mirrors to offer a

compromise between portability and flexibility, even

if they are more costly and complex. Future

telescopes seem bright with advances in segmented

mirrors, adaptive optics, and space-based

observatories outside human reach. Using artificial

intelligence-powered data processing and

interferometry will help to explore far-off and dim

celestial objects. These developments will help to

better understand the universe and enable important

discoveries as well as a clearer knowledge of its

fundamental components.

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