November 18, 2019 0

هواية الفلك في عشرة دقائق، انواع التلسكوب Amateur Astronomy in Ten Minutes, Telescope Types


Welcome to anew episode of Amateur Astronomy In Ten Minutes We’ll talk in this episode Telescope Types and how to choose Telescope could be used in two ways for astronomy 1. Visual observation using an eyepiece This is an interactive and exciting way to view celestial objects directly many telescope types could be used what is advised for beginners is to use an ALT-AZIMUTH NEWTONIAN telescope, DOBSONIAN Type it consists of two mirrors, primary concave that magnifies light and secondary flat that reflects light into the eyepiece or camera sensor Price range for Newtonian Dobsonians is affordable and competitive compared to other telescope types and they are easy to use You can get a good deal for a large mirror that could be used to see faint objects especially if you take it to a dark sky area You can make your own Dobsonian telescope using components from your favorite hardware store You can bye mirrors and make the scope or you can make your own mirror 2. Astrophotography Astro imaging needs precision and advanced tools but you can start with simple projects to obtain decent results with simple tools Telescopes has two major parts 1. Optical Tube Assembly (OTA) which contains lenses or mirrors or both 2. Mount A. Electrical mount, that could track the sky and contains GPS system and a computer that has a saved sky map that telescope can use to find celestial objects(you have to provide time, date and location) B. Manual mount, uses manual to direct the scope to a target Manual mounts are used for visual observation using an eyepiece not with a camera Manual method provides huge excitement spending time using your sky map to find your target in the sky then directing your scope to the sky There is a rush of joy that embraces you when you find your target manually I advice beginners to start with the manual method lets start with the Optical Tube Assembly (OTA) 1. Refractor Telescope or lens using telescope lenses focus light at the focus point lenses suffer from Chromatic Aberration lenses separate light colors distorting the image this was overcome by using a second lens making Achromatic Doublet for the best image 3 lenses are combined in Apochromatic Triplet reinstating the separated colors to one image The type of lens glass has a great effect on image quality the best is extra low dispersion glass (ED) in conclusion the best lens telescope is for visual observation or imaging is Apochromatic Triplet ED one issue with a lens scope the larger the focal length the telescope length increases which could cause an issue for transportation and storing and increases the telescope weight weight could be solved by using carbon fiber material Carbon fiber is light and strong and it does not expand or retract with heat change which is important to have a stable focal length the larger the diameter of the scope it can gather more light especially for faint objects the least diameter for a scope for faint object observing is 4 inchs bright objects like the moon and some planets does not need a large aperture scope 2. Reflective Telescope or mirror telescope mirrors are cheaper than lenses you can get a larger scope with mirrors for a cheaper price compared to lens scope Mirrors suffer from Spherical Aberration Spherical mirros focus light at different points this is overcome by using Parabolic Mirror, which has one focus point there are two major reflective telescopes A. Newtonian B. Cassegrain Newtonians has two mirrors(مرايا وليس عدسات), primary parabolic concave which magnifies light and reflect it to a secondary flat mirror which reflects light to the eyepiece or camera sensor there is a focus and prime focus prime focus point is used for imaging with a camera which is closed to the secondary mirror while the regular focus is farther from the secondary mirror in comparison which is used by the eyepiece this is important when you obtain a newtonian telescope because if you are acquiring it for imaging it should be and Astrograph type regular Newtonians could be used for imaging too by pushing the primary mirror closer to the secondary mirror or by using a Barlow lens other issue with Newtonians include Coma periphery of images are distorted this is overcome by using Coma Reducer or by cropping the image without a coma reducer also Newtonian images has Diffraction Spikes caused by the Spider which carries the secondary mirror (also happens in Ritchy Chretien telescopes) Dobsonian Newtonians are easy to use Dobsonians are Newtonians first made by John Dobson to reduce the scope price and ease of use Dobsonian mount is Alt/Azimuth mount easy to assemble and use usually is a wooden box allowing the scope to slide/rotate on Altitude and Azimuth directions to point to the target to reduce weight, improve transportation and storage feature Truss tube is used also improved rigidity mounts has weight capacity telescope functionality depends on its weight, the lighter the better B. Cassegrain Refractors which has 3 types Schmidt-Cassegrain it has two mirrors, one parabolic and the other hyperbolic could be used for observation or imaging to focus Primary mirror’s position is adjustable(could create flexure issues) it has a corrector plat Corrector plate at the front is flat it reduced spherical aberration of the parabolic mirror second type of Cassegrain is Maksutove which has a concave corrector plate in the front (there is a Newtonian Maksutove too) the third Cassegrain type is Ritchy Chretien those are made of two hyperbolic mirrors used for astroimaging like the Hubble space telescope Next episode we’ll discuss telescope Mounts

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