* Astronomy

TeleVue Paracorr is a universal corrector that tightens and intensifies star images on all f-ratios from f/3.5 to f/8 without adding any false colour or spherical aberration. You no longer have to constantly shift a Dobsonian to keep objects centred for sharp viewing. Using a Tele Vue eyepiece, put M-13 at the edge of the field and enjoy resolving its beauty as it drifts across your view.
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Coma makes stars look like blurry comets whose tails point out radially from the center of the field. The faster your scope's speed, the worse the effect. All parabolic mirrors used in Newtonian reflecting telescopes are limited in field sharpness due to coma. Even a perfectly made 13" f/4.5 parabola has only about 0.1 degree diffraction limited field.
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Ed ~ ParaCorr stands for 'parabolic corrector'.

See also OCS System