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Below is a table of advantages and disadvantages of different types of telescopes. The writing in red is in the wrong place can you put it into the correct place on the table? Type of telescope Refractor Advantages Disadvantages Easy to use and reliable with little or no maintenance. High contrast images with no secondary mirror or diagonal obstruction. Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters. Colour correction is good. Sealed optical tube reduces image degrading air currents and protects optics. Objective lens is permanently mounted and aligned More expensive. Heavier, longer and bulkier. Focal ratios are usually long making photography of deep sky objects more difficult. Some colour aberration in achromatic designs (doublet). More expensive than Newtonians of equal aperture. Reflector Newtonian Lowest cost since mirrors can be produced at less cost than lenses in medium to large apertures. Reasonably compact and portable. Best all-around, all-purpose telescope design. Reasonably good for lunar and planetary work but good for deep sky astrophotography. Low in optical aberrations delivering a very bright image. Slight light loss due to secondary (diagonal) obstruction when compared with refractors Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae because of practical aperture limitations. Reflector Cassegrain Excellent for lunar, planetary and binary star observations. Good for distant terrestrial viewing. Excellent optics with razor sharp images over a wide field. Useful for all types of photography. Closed tube design reduces image degrading air currents. Most are extremely compact and portable. Easy to use, durable and virtually maintenance free. Large apertures at reasonable prices and less expensive than equivalent aperture refractors. Best near focus capability of any type telescope. Most versatile type of telescope. It is not what people expect a telescope to look like. Slight light loss due to secondary mirror obstruction compared to refractors. Generally not suited for terrestrial applications.