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There Is Many Brand And Different Type Of Design Of Telescope. Basic Function Of A Telescope Is To Magnify The Object Seen And Also To Amplify The Brightness Of Object Seen. The Heart Of A Telescope Is The Mirror Lens That Collect The Light


Basic Understanding Of Telescope

  1. Design Of Telescope - Telescope Have 3 Primary Different Design : Refractor, Reflector And Also Catadioptric
  • Refractor Are The Most Simple Design, Involving Focusing Incoming Light Source To A Single Point. Large Objective Lens Gather Light And Focus It To Increase Image Detail And Brightness.

Refractor Telescope

  • Refractor Provide The Highest Contrast View Because Of No Central Obstruction, But Due To Design That Causes Light Refraction, This Will Scatter Light Of Different Colour Spectrum Resulting Chromatic Aberation (Colour Fringing) Best Optical Refractor Design Using Special Glasses Will Elimated This Problem But Will Be More Costly Per Aperature

Chromatic Aberation Seen As Blue/Brown/Purple Colour Fringing

  • Reflector Are Basically Reflection Mirror. Precision Polish Reflecting Mirror Will Focus Light From Mirror To Increase Image Brightness And Detail. Mirror Are Easier To Manufacture And Cost Less Than Lens (Bigger Aperature For Price). Reflector Does Not Suffer From Chromatic Aberation And Provide Almost Similar Contrast To Refractor. A Reflector Can Be Built With Spherical Or Parabolic Mirror. A Parabolic Mirror Can Give Diffraction Limited Optics But Cost More. A Spherical Mirror Gives Good Image If Focal Ratio Exceed F/10, Anything Under Will Require A Spherical Lens Corrector (Known As Jones-Bird Newtonian)

Reflector Telescope

  • A Catadioptric Are Combination Of Refractor And Reflector. This Design Allow A More Compact Telescope For Aperature. It Is Also Provide Chromatic Aberation Free Image. Catadioptric Design Has Relatively Large Central Obstruction And Might Reduce Contrast Slightly (Basic Theory Is 28% Reduction In Brightness & Contrast For SCT, 18% In Maksutov Cassegrain & 20% In Visual Reflector)

Catadioptric Involve Folding Optical Path Multiple Time To Achieve Compact For Aperature Telescope

Catadioptric Telescope


  1. Factor Determining A Telescope Performance
  • Important Determination Of Telescope Performance Is Always Aperature (Size Of Telescope Objective) A Bigger Aperature Allow Higher Light Collection And Image Resolution.
  • Central Obstruction Determine The Contrast And Brightness Of Image
  • Light Gathering Power Is Determined By Aperature Of A Telescope. A Higher Light Gathering Power Translate To Brighter Image Of Deep Space Object.
  • Resolution Of Telescope Is Determined By Aperature Of A Telescope. Resolution Of Telescope Is Measure By Dawes Limit (Typical In Arc Second) A Smaller Dawes Limit Translate To Better Capability Of Telescope To Detect And Differentiate Fine Detail Of Objects
  • Optical Coating : A Multi-Coated Lens Will Reduce Light Loss From Reflection Of Glass. In A Refractor Telescope, Uncoated Glass Gives About 8% Light Loss, Where As Best Multi-Coated Refractor Only Loss Less Than 0.5% Of Total Light. In Case Of A Reflector, The Coating Quality Will Depends On Type Of Aluminium Used And Measured In Reflectivity Index. The Best Reflectivity Index Is 99% Reflectivity
  • Optical Perfection : A Mirror Or Lens Perfection Is Calculated Based On Diffraction Limit. A Diffraction Limited Optics Translate To Almost A Perfect Mirror, Where The Maximum Resolution Is Possible With Usage Of Diffraction Limited Lens/Mirror.
  • Spherical Aberation : A Mirror Or Lens Causes Deviation Of Light Pathway. A Spherical Imperfection Is Common In All Type Of Telescope Design, Unless Fully Corrected. The Lowest Commercial Minimum Spherical Aberation Telescope Are Maksutov-Cassegrain Design


  1. Maximum Performance Of Telescope And How It Is Calculated
  • Magnification : Maximum Magnification Of A Telescope Is Calculated Based On Aperature Of Telescope. A General Rule Of 50-60x Per Inch (25.2mm) Of Aperature Is The Maximum Magnification Of a Given Telescope. A 50mm Telescope Will Have 120x Maximum Magnification. A 203mm (8'') Telescope Will Have 480x Maximum Magnification
  • Light Gathering Power : Light Gathering Power Will Translate To How Bright An Object Seen Via Telescope. Higher Light Gathering Power Allow Dimmer Objects Seen Brighter And With More Detail. Light Gathering Power Is calculated Based On Aperature (Size Of Telescope Lens/Mirror) A 70mm Telescope Has 70x70/49 : 100x Light Gathering Power. A 203mm (8'') Telescope Has 203x203/49 : 841x Light Gathering Power. Higher The Light Gathering Power, Brighter A Deep Space Object Will Be Seen