BSL – Types of telescopes

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Telescope Basic

There days are three main types of telescopes
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Tube assembly and light path of three types of telescopes
(Refractor / Reflector / Cassegrains)
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(1) Refractor

Uses lenses
They are low maintenance, tend to be smaller and very light weight, hence they are very portable.
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(2) Reflector

Uses mirrors
Most reflecting telescopes on the market are made in the Newtonian design, where you see the eyepieces placed near the front of the tube, rather than the back.
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(3) Cassegrains
Uses both – lenses & mirrors
Essentially, reflection and refraction are combined into a single system.


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Essentially modern telescopes fall into two categories

Automated models :- GOTO / GPS
or
traditional manual telescopes.

Both require some knowledge of the Night Sky!
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People often ask me “which telescope?”
to want to own a telescope.

Telescopes do NOT really matter whether you have a large or small budget.

What`s important is that you choose a telescope that satisfies your needs
and initial abilities successfully so that you enjoy this engaging hobby that is astronomy!
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(1) Refractor

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  • Use objective lens (no mirror) to collect and focus light.
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  • This is one of the oldest models of telescopes and widely used.
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  • These design is seen mostly in the beginner scopes.
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  • They have an aperture lens and an eyepiece at the ends.
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  • Experts for the Moon and planets.
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Pros

  • It has fantastic revolving power.
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  • The performance is satisfying even in inferior conditions.
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  • Light never reflects in this tube assembly.
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  • The optical alignment is nearly permanent so you do not need to have headache on maintenance.
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  • The design and eyepiece is simple.
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  • It has long focal ratios that means longer focus.
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Cons

  • The cost is higher than the reflector telescopes.
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  • Expensive at large apertures.
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  • Chromatic aberration and blurring if it is not corrected which causes change of colour of the image.
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(2) Reflector (Newtonian)

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  • Collect light with a primary mirror and flat secondary mirror.
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  • The reflector telescopes designed by Newton do not use lens, it uses mirror.
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  • A small flat secondary mirror is used here to direct the light to the eyepiece.
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  • Lasting throughout the year or through many years.
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Pros

  • It has better light collection ability than the refractors as it has large mirrors.
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  • Large apertures – Dobsonian possible.
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  • No chromatic aberration.
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  • The cost is relatively low.
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  • Only low levels of obstruction.
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  • Very many models available.
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Cons

  • Optical quality is sometimes disappointing and not very good for astrophotography.
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  • You have to collimate it before use and take of mirror cleaning timely.
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  • The tube is open, so you have to take care of the dusts and humidity.
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  • A little bit bulky and heavier.
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(3) Cassegrains

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  • This design uses a spherical mirror – most importantly it ha a curved and thin piece of glass at the very front that helps to correct the output of spherical mirror.
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  • Cassegrain telescopes are unique as they use a primary mirror, but with a hole at the centre. It can direct the light towards the back.
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  • The secondary mirror is a concave mirror, i.e. not flat like newtonian. It enhances the focal length and in turn provides better performance.
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  • Cassegrain telescopes are not widely available like the other two mentioned before.
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  • Schmidt Cassegrain and Maksutov telescopes are made based on this design and they are also very popular.
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  • Compact and easy to transport.
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Pros

  • This is great for sky observation and astrophotography.
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  • The optics can be folded that makes it lighter and shorter.
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  • It has a focal reducer so that you can use it in versatile purpose.
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  • High viewing comfort.
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Cons

  • It is expensive.
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  • Views are narrower and exposures are longer.
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  • The contrast is less and sometimes need collimation.
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  • Larger secondary mirror/obstruction than a Newtonian telescope.


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