Which Telescope Should I Buy?

If you go out to any telescope store you will see many stores owner will try to sell you a small and cheap telescope by saying it has 600X magnification and it can show craters in moons, Jupiter's belt, Saturn rings, etc... not only this they will also show you the original box which has wonderful colored pictures of planets, galaxies, nebulae and much more. Beware of all these telescopes because the wonderful colored pictures that you saw in original box was all taken from Hubble Space Telescope. In real it will not look like the pictures you saw in original box. This will hurt your interest and curiosity of being a Amateur Astronomer. Due to this reason many new comers who comes to astronomy worlds get hurts and leave the wonderful astronomy world without knowing the real facts. So, always be aware not to fall into the trap of those telescope stores owners. 

Before buying your first telescope keep in mind few things

1. Never buy any telescope without knowing anything about it. I suggest you to visit your nearest astronomy clubs. Look through different peoples telescopes with different eyepieces to know what eyepieces are and what they do. Discuss with them what you want to see they can help you out in getting a good telescope.

"For ex - Watching moons craters, planets, planetary details like watching Jupiter's belts, Saturn's ring or interested in Deep Space Objects (DSO's) like galaxies, nebulae, star clusters or something like this."

The best thing is that without wasting your huge money just buy a used telescope and learn something from it and plan for your future one which you really want and at best price.

2. Never buy your telescope from a toy store or from a un-reputable seller. You may get some telescope at cheaper price but their optics quality will be very very poor and this will disappoint you and nothing else. So, always select your telescope from a reputable dealer.

3. Never fall into the trap of a seller who is convincing you to buy a telescope which he is claiming to be of superior quality. Its always better to visit your nearest astronomy clubs. Look through different peoples telescopes with different eyepieces to know what eyepieces are and what they do. Discuss with them what you want to see they can help you out in getting a good telescope.

4. Always visit to reputable telescope dealer who has good knowledge about it. A good dealer will ask your requirements and he will give his best to choose a telescope you need.

All the informations mentioned above should be followed.

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Before buying any telescope you should know few important things about it. Without having proper knowledge it is foolish to buy any telescope.

Aperture

Aperture is the most most important part of any telescope. Get the bigger aperture till you can afford it. Aperture is the diameter of the mirror or lens that collects light. In simple words, just compare it with our eyes. We cant see much distant planets because they are far away and when it comes to galaxies, they the most far away objects. Our eye is unable to see them because the light coming from distant planets or galaxies is beyond our eye range. Our eyes can not collect enough light from distant objects as it is small. We need certain things that work as a bigger eye, which we call it as mirror or lens. 

The bigger the diameter of mirrors or lens the more light it collects. Lens or mirrors works as a big eye and collects light from distant objects. The more light it collects the more details of that objects we can see.
Its simple!!!!

Magnification of any telescopes depends on its aperture. Large aperture collects more light and gives higher magnification and greater resolution(good quality images). So, those cheap telescopes offering high magnification will show some satisfactory view of nearer objects like Moon along with its craters, Jupiter along with its four moons, etc.... but those distant object will look fuzzy because these cheap telescopes aperture is not large enough to support high magnification and to show vivid details of that distant objects.

So, always keep in mind to go for larger aperture. Get the bigger aperture till you can afford it.

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Eyepiece

Types Of Telescopes

There are three main optical types:
 
The refracting telescope which uses lenses to form an image.
The reflecting telescope which uses an arrangement of mirrors  to form an image.
The catadioptric telescope which uses mirrors combined with lenses to form an image.

There is also different types of telescope like:

    Radio telescopes
    X-ray telescopes
    Gamma-ray telescopes
    High-energy particle telescopes

 Those telescope mentioned above are used for studying different types of rays present in the universe. We dont use them for our satisfying purposes, only scientist present in NASA  uses it.

So, by now you came to know that which telescope we generally use, but still i would like to mention them are:

    The refracting telescope
    The reflecting telescope
    The catadioptric telescope

Catadioptric Telescope

Catadioptric or compound telescopes use both lenses and mirrors. The most popular design is the Schmidt-Cassegrain, which burst onto the market in the 1970s and quickly gained a place for itself alongside refractors and reflectors, which had been around for centuries. The following comments apply primarily to Schmidt-Cassegrains. 

Advantages

The pluses of the "Schmidt-Cass" are in portability, convenience, and special options such as advanced tracking and electronics -- not visual performance. While most people can haul an 8" reflector in and out of doors, it is awkward and heavy. Most 8" Schmidt-Cassegrains come in a padded footlocker that can be hoisted with one hand. (The tripod is separate.) The footlocker can be stowed in a car trunk or closet like a large piece of luggage, whereas a reflector tends to displace everything around it.
A Schmidt-Cassegrain's relatively short tube allows a motorized mounting to track the stars more reliably, making astronomical photography less difficult (it's never easy). These are excellent photographic telescopes. Elaborate electronic drive controls are available as options on Schmidt-Cass mountings for photographers and CCD camera users. Some can be bought with robotic computerized pointing capabilities. 

Disadvantages

The image formed by a Schmidt-Cassegrain will probably be a touch less sharp than the image formed by a good reflector of the same aperture. This is most noticeable when observing planets. The cost is higher than for a reflector of the same aperture. A right-angle mirror (star diagonal) is generally used at the eyepiece to provide a comfortable viewing position, and this means your view is mirror-reversed. The focusing mechanism can be a bit sloppy and imprecise. You can't take the scope apart yourself; major adjustments mean shipping it back to the factory.

Or

Catadioptric telescopes are essentially a combination of a refractor and a reflector. There are 2 very popular flavors widely available in today's telescope marketplace. One is the Schmidt-Cassegrain, and the other is the Maksutov-Cassegrain (see images below). These telescopes fold the light path 3 times allowing for a much shorter tube. Because of their clever use of corrective lenses and lack of a spider to hold the secondary mirror, they are free of many of the optical defects present in refractors and reflectors.
Light enters the front of the tube through a corrective lens. The light then travels down the tube to the primary mirror. From there, it is reflected up the tube to a secondary mirror which in turn reflects the light back down the tube to the focal plane.

 The focusing mechanisms of Catadioptric telescopes are different than in reflectors and refractors. Instead of moving the eyepiece in and out of the focal plane, the whole primary mirror is moved in and out. Because of their more complex design, their tube construction and mount are generally very well thought out and implemented. Most of them are wonderful telescopes.

Catadioptric telescopes can be very expensive, but a well-built Catadioptric telescope is quite simply a joy to own and use.

Refracting Telescope

Refractor Telescopes

The refractor telescope uses a lens to gather and focus light. The first telescopes built were refractors. The small telescopes sold in department stores are refractors, as well as, those used for rifle scopes.

Advantages

 

1. Refractor telescopes are rugged. After the initial alignment, their optical system is more resistant to misalignment than the reflector telescopes.
2. The glass surface inside the tube is sealed from the atmosphere so it rarely needs cleaning.
3. Since the tube is closed off from the outside, air currents and effects due to changing temperatures are eliminated. This means that the images are steadier and sharper than those from a reflector telescope of the same size. 

 Though excellent refractors are still made, the disadvantages of the refractor telescope have blocked the construction of very large refractors for use in astronomical research. 
 

Disadvantages

All refractors suffer from an effect called chromatic aberration (``color deviation or distortion'') that produces a rainbow of colors around the image. Because of the wave nature of light, the longer wavelength light (redder colors) is bent less than the shorter wavelength light (bluer colors) as it passes through the lens. This is used in prisms to produce pretty rainbows, but can it ruin an image! 

 There a couple of ways to reduce chromatic aberration. One way uses multiple compensating lenses to counteract chromatic aberration. The other way uses a very long objective focal length (distance between the focus and the objective) to minimize the effect. This is why the early refracting telescopes were made very long. 

 

1. There a couple of ways to reduce chromatic aberration. One way uses multiple compensating lenses to counteract chromatic aberration. The other way uses a very long objective focal length (distance between the focus and the objective) to minimize the effect. This is why the early refracting telescopes were made very long.
2. How well the light passes through the lens varies with the wavelength of the light. Ultraviolet light does not pass through the lens at all.
3. How well the light passes through decreases as the thickness of the lens increases.
4. It is difficult to make a glass lens with no imperfections inside the lens and with a perfect curvature on both sides of the lens.
5. The objective lens can be supported only at the ends. The glass lens will sag under its own weight.

Reflecting Telescope

Reflector Telescopes

The reflector telescope uses a mirror to gather and focus light. All celestial objects (including those in our solar system) are so far away that all of the light rays coming from them reach the Earth as parallel rays. Because the light rays are parallel to each other, the reflector telescope's mirror has a parabolic shape. The parabolic-shaped mirror focusses the parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope.

Advantages

1. Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way.
2. Support for the objective mirror is all along the back side so they can be made very BIG!
3. Reflector telescopes are cheaper to make than refractors of the same size.
4. Because light is reflecting off the objective, rather than passing through it, only one side of the reflector telescope's objective needs to be perfect

 

 

 Alas! Despite the advantages of the reflector telescope, astronomers must contend with some minor annoyances.

Disadvantages

1. It is easy to get the optics out of alignment.
2. A reflector telescope's tube is open to the outside and the optics need frequent cleaning.
3. Often a secondary mirror is used to redirect the light into a more convenient viewing spot. The secondary mirror and its supports can produce diffraction effects: bright objects have spikes (the ``christmas star effect'').

Summary of Telescope

 What exactly is a telescope?

The simplest definition is; an instrument that gathers light and focuses that light into an image. In turn, this image can be magnified. This instrument is also mounted in such a way that allows you to swing it from object to object. Let's break this down further.

A telescope's ability to gather light is dependent on:

Aperture ... the larger the primary optics (the largest lens or mirror) the more light is captured.

Optical quality ... the more reflective a mirror and the more a lens allows light to pass through it, the more light is transmitted to your eye.

Contrast ... the more absorptive the inside surface of the tube is, the less light will bounce around in that tube, which leads to improved contrast (darker backgrounds).  A darker background means that you see more of the object you are looking at. An improperly designed optical assembly can also rob you of contrast.

Collimation (alignment) ... even if you have the best optics, if they are not properly aligned, your light gathering capacity will be diminished.

A telescope's ability to focus properly is dependent on:

Collimation ... how well the optics are aligned.

Optical quality of the eyepieces

Focusing mechanism ... a focuser that is smooth and allows for minute adjustments is necessary. This focuser must also be aligned properly to perform at its best.

A telescope's mount needs at a minimum the following characteristics:

Stability ... the telescope should not sway or bounce on the mount.

Rigidity ... when you move or focus the telescope, the stand should be solid enough to quickly dampen out any vibrations, otherwise these vibrations will be seen in the eyepiece. A poorly designed mount or a mount that is too small to handle the weight and size of a telescope can render even the best telescope useless.

Smooth motions ... the mount should move smoothly from object to object.

Telescope types and how they work

The Refractor

The refractor telescope has been around for centuries. In 1610, Galileo used a small refractor to watch the phases of Venus and observe craters on the moon. With it he discovered the first 4 moons of Jupiter and observed Saturn's odd shape. Galileo's telescope had a 2" aperture, quite small by today's standards, and was, shall we say, optically challenged. Because of this lack in optical quality, he could not resolve that Saturn's strange shape was actually caused by its rings. Approximately 50 years later, improvements in optical quality allowed observers to determine that Saturn's odd shape was actually a big ring (rings) around the planet.

To refract means to bend. Light enters through the lens at the front of the tube. This lens is called the objective. The light is refracted down the length of the tube where it eventually reaches its focal plane ( where the light becomes focused at a specific point). There, an eyepiece mounted in a focuser, allows that light to be magnified into an observable image. Simply put, the better the quality and alignment of the optics, the better the image produced by a refractor will be. Actually, this statement holds true for all telescopes.

Refractors are a very versatile instrument. With the right eyepieces, they can be used for both daytime and nighttime observing and given good optics, deliver superb detail. Small ones are also very portable. Unfortunately, high quality refractors tend to be very pricey due to the cost associated with producing high quality optics. One of the downfalls of inexpensive refractors is that for astronomical viewing, they have the tendency to add false color to images. This is called chromatic aberration. These colors usually take the form of a pale violet halo around the observed object. Don't let this scare you off though. There are many excellent entry level refractors that will perform beautifully. Many observers swear by their refractors and believe them to be unrivaled for sharp lunar, planetary and binary star observing.

The Newtonian Reflector  

The reflector is a telescope design invented by Isaac Newton in the 1660s. Rather than lenses, the reflector  uses 2 mirrors to bring light to the eyepiece. Light travels down the tube to the primary mirror, which is the larger of the 2 mirrors. The primary mirror is generally a paraboloid (concave) mirror. It reflects the light back up the tube to the secondary mirror. The secondary mirror is an ellipse with a flat surface which is mounted at a 45 degree angle on a device usually called a spider. The light is reflected from the secondary mirror to the eyepiece where it can be magnified into an observable image.

Dollar for dollar, reflectors offer the most aperture. They produce sharp images that are free of any added color.  Optically speaking however, they have 2 things going against them:

1) The spider holding the secondary mirror forms a central obstruction that produces a diffraction pattern. This is most noticeable at high magnifications on bright objects. Look at the image below. Notice the 4 spikes coming away from the bright star in the center? This is the diffraction pattern caused by a 4-vane spider.

2) Because of the shape of the primary mirror, reflectors suffer from a condition called coma. This has the effect of making objects at the outside edge of the field of view to have the appearance of being wedge shaped or look like little comets. This really is not that big a concern for visual observation as the effect is most noticeable only at the outside most part of the field of view and not present at all in the central field of view which is where most of your observing is done anyway. Also, some eyepiece designs work well to counteract this effect.

Again don't let these characteristics scare you away from a reflector. Consider this, many big telescopes in observatories around the world are reflectors.

While there is no such thing as a perfect telescope, for visual observing a well designed 6"  f/5  to f/7 reflector with good mirrors that are kept in alignment (collimated) on a Dobsonian mount (see mounts section bellow) is, in our opinion, a superb instrument that will give you years of use and not break the bank. It will deliver good views of the moon and planets and has enough light gathering power to reveal many deep sky objects given dark skies and good seeing.
Catadioptric telescopes are essentially a combination of a refractor and a reflector. There are 2 very popular flavors widely available in today's telescope marketplace. One is the Schmidt-Cassegrain, and the other is the Maksutov-Cassegrain (see images below). These telescopes fold the light path 3 times allowing for a much shorter tube. Because of their clever use of corrective lenses and lack of a spider to hold the secondary mirror, they are free of many of the optical defects present in refractors and reflectors.

Catadioptric Telescopes

Light enters the front of the tube through a corrective lens. The light then travels down the tube to the primary mirror. From there, it is reflected up the tube to a secondary mirror which in turn reflects the light back down the tube to the focal plane.

The focusing mechanisms of Catadioptric telescopes are different than in reflectors and refractors. Instead of moving the eyepiece in and out of the focal plane, the whole primary mirror is moved in and out. Because of their more complex design, their tube construction and mount are generally very well thought out and implemented. Most of them are wonderful telescopes.

Catadioptric telescopes can be very expensive, but a well-built Catadioptric telescope is quite simply a joy to own and use.