In the last blog, we covered the history of the Newtonian reflector, its inherent aberrations, and how Tele Vue’s Paracorr enlarged the “sweet spot” of fast scopes to cover the entire field. We also compared the Paracorr – Newtonian combination against more “exotic” telescope designs for imaging. If you missed it, you can read Part 1 before continuing.
Which Paracorr to Use? Over the years there have been two optical versions of the Paracorr. The original Paracorr came in various mechanical designs which developed as we developed new eyepieces. For this BLOG, we’ll focus on the currently available three versions of the Type-2 Paracorr: 2″ Photo/Visual, SIPS, and 3″ Photo models. Performance improvement over the original Paracorr is most noticeable on all Newtonian/Dobsonian telescopes of f/4.5 and faster.
Paracorr and the Evolution of Newtonian / Dobsonian Telescopes
Invented from lenses used to make eyeglasses, refractors were the first telescopes when introduced in the 1600s. However, the early refractor builders could not avoid building scopes that displayed color fringes (chromatic aberration) around bright objects. It was Sir Isaac Newton (1642–1727) who figured out that white light is composed of different wavelengths that we see as colors. Each wavelength will refract (bend) by a different amount as it passed through the refractor’s objective glass. The longest wavelengths (red) refract less while the shorter wavelengths (blue) refract more. As a result, the red component of the image focuses behind the blue component. Pinpoint images and higher magnification were out of the question with these primitive scopes. Even after the cause of chromatic aberration was revealed, refractor builders didn’t have the glass types and manufacturing skills to counter it for another century. Sir Newton, however, had an idea to build a second type of telescope that avoided refraction: a reflector.
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