This unique design offers large-diameter optics while maintaining very short tube lengths, making them extremely portable. The Maksutov-Cassegrain (Mak) optical system uses a combination of mirrors and lenses and is referred to as a compound or catadioptric telescope. With larger Dobs, the base itself can be heavy and bulky.Dobs and other alt-az mounted Newtonians are more difficult to motorize and many may not track at all.Planetary imaging may require very high power 3x-5x Barlows to obtain to suitable focal length for many cameras.Additional coma corrector optics are needed for best performance for deep sky photography.Fast Netwonians (f/6 and lower) need optics to be collimated regularly.Very bulky and heavy in 10" and larger sizes.Generally not suited for terrestrial observing due to visual images being inverted (upside down and backwards).Newtonians with a focal ratio of f/6 or lower suffer from coma, an off-axis aberration that causes images to flare inward and towards the optical axis (stars take on a "comet-like" shape).The location of a Newtonian’s secondary mirror and struts (the support structure for the mirror) creates a central obstruction and causes the appearance of diffraction spikes.When visual observing with large Dobs, the tube orientation can sometimes put the eyepiece in a poor viewing position, requiring a ladder to access it.Reasonably good for lunar and planetary work, but larger apertures are better for deep sky objects.When used with a Dobsonian mount, reflectors are very simple to operate targets can be found quickly by star hopping.Generally very little issue with dew except in very high humidity. The eyepiece is located at the top end of the telescope allowing for a much more compact mounting system, reducing cost and adding portability.Short focal ratio (f/4 to f/8) offers a wider field of view.Reasonably compact and portable up to focal lengths of 1000mm.Because mirrors are less expensive to produce than lenses, Newtonian telescopes are usually less expensive for any given objective diameter (or aperture) than comparable refractor telescopes. 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.
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