In turn, the secondary mirror reflects the image out of an opening at the side of the front end of the main tube and into the eyepiece. Newtonian Reflectors, including the Dobsonian (Dob), have a concave spherical or parabolic primary mirror at the back of the telescope that collects and focuses incoming light onto a flat secondary (diagonal) mirror. Some color aberration in achromatic designs (doublet).Focal ratios for traditional refractors are usually long (f/11 or slower), making photography of deep sky objects more difficult (short focal length apochromats are now available that change this limitation, but their magnification is limited).Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae because of practical aperture limitations.Cost and bulk factors limit the practical useful maximum size objective to small apertures.Heavier, longer, and bulkier than Newtonians and catadioptrics of equivalent aperture.More expensive per inch of aperture than Newtonians or catadioptrics.Objective lens is permanently mounted and aligned-fixed collimation.Sealed optical tube reduces image degrading air currents and protects optics.Color correction is good in achromatic designs and excellent in apochromatic, fluorite, and ED designs. High contrast images with no secondary mirror obstruction.Excellent for lunar, planetary, and binary star observing especially in larger apertures.Easy to use and reliable due to the simplicity of design.Refractors are the traditional optical design that the average person instantly visualizes when he or she hears the word "telescope".Light passes through the refractor in a straight line from the front objective lens directly to the eyepiece at the opposite end of the tube. Refractor Newtonian Reflector Maksutov-Cassegrain Schmidt-Cassegrain EdgeHD Rowe-Ackermann Schmidt AstrographĪ Refractor is a long, thin telescope. In this guide, our experts break down each telescope type so you can make the best decision based on your wants and needs. From refractors to reflectors to Cassegrains-there are so many telescope optical designs to choose from, each with its unique advantages and disadvantages.
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