Best apochromatic refractor telescope free#

The best refractors, free of chromatic aberration or optical defects and made for both imaging and visual astronomy, have eye-popping prices – often several thousand dollars for something just 3” or 4” in aperture.

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Inexpensive refractors are almost always achromats which require long focal ratios and, consequently, long tubes and narrow fields of view to minimize chromatic aberration – the ugly purplish halo around bright targets caused by the inability of the objective lens to focus all colors to the same point.Īpochromatic refractors are heavier and more costly, with many often still suffering from some chromatic aberration – particularly those made for imaging. The cynical would say that the definition of an astronomer is someone willing to spend a fortune to make a little ring of purple go away – and they’d be right. Chromatic aberration – Apart from their small apertures, chromatic aberration is the bane of refractors.Meanwhile, a 10” Dobsonian can be easily carried in one piece and costs less than a 6” refractor and mount. 7”, 8”, or even 9” refractors pop up occasionally but often cost as much as a sports car or even a home, and usually need a permanent observatory to support them. You can’t get a big one – Commercial refractors top out at 6” in aperture, and most of these are enormous instruments that rival a 12” catadioptric or 16” Dobsonian in bulk and cost.This is not to say, however, that refractors don’t have their disadvantages among them: However, at low power field curvature can be a nuisance (even more so when imaging) and cheap eyepieces may worsen chromatic aberration in achromatic instruments. More friendly to inexpensive eyepieces – Refractors don’t suffer from coma, edge-of-field astigmatism, or collimation errors like a Newtonian, meaning cheaper eyepieces tend to work better with them.Their slightly higher contrast can also help on certain large nebulae and other deep-sky objects. Wide fields of view – Small refractors tend to more commonly come with fast focal ratios and 2” focusers, which make them great for low-power sweeping.However, you still need a field flattener and/or reducer for best results, as well as a beefy focuser that won’t slip or flex under heavy loads. They also tend to have fast focal ratios when made for astrophotography and work well with focal reducers. The weight of a camera is on the back of the tube instead of the side. Simplified astro-imaging – Refractors don’t have the razor-sharp collimation requirements of a Newtonian reflector, nor do they have mirror flop or image shift.Refractors seldom have issues with their lens coatings degrading over time and will never become nearly useless the way a reflector can with a degraded primary mirror.

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They do not suffer from warm air rising through the tube and causing “tube currents” like a reflector or catadioptric. Big refractors may need some time for their lenses to acclimate to cooler temperatures, but small refractors need little. Convenience – Refractors require negligible amounts of care when it comes to preserving the optics, collimating them, and of course, cooling down.Higher performance – With no mirror coatings to scatter light, no secondary mirror to smear out diffraction rings, and the ability to add baffling to control stray light, refractors are more efficient with their aperture – which is usually small.Ī refractor typically punches above its weight class in terms of image brightness, contrast, and resolution by about an inch or two of aperture compared to catadioptric and reflecting telescopes which use two or more mirrors to create an image.Refractors have a number of advantages over reflectors and catadioptrics, such as: Buy on High Point Scientific Buy on OptCorp Advantages of a Refractor Telescope

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