TeleVue Paracorr Visual with Tunable Top

TeleVue Paracorr Visual - 2 Inch Format - Includes 1-1/4 Inch Adapter - Tunable Section - Brass Clamp Rings
Concept: I have built Newtonian reflectors since my high school days and still enjoy observing with my 12" f/5.3. Knowing how the Nagler eyepiece complemented fast Dobsonians and Newtonians by removing eyepiece induced astigmatism, I now became intolerant of the inherent defect of coma in a parabolic mirror.
Paracorrmore stars, sharper stars, more time to observe.
I decided to try to achieve the same field quality for parabolas as reached by my Nagler eyepiece and 4-element refractor designs. Existing coma correctors seemed to be limited in color correction, spherical aberration and convenience in use. Paracorr (parabola corrector) uses 2 multi-coated, high-index doublets, is completely color-free, center and edge, and installs like a Barlow. Coma is corrected so well, the diffraction limited field area of an f/4.5 Dob/Newt is increased 36 times! - Al Nagler
An optical chain is as good as its weakest link. With the development of 82 degree Nagler eyepieces, Tele Vue offers the largest, flattest and best corrected visual fields in the industry. Combine the Nagler revolution, Dobsonian revolution and Paracorr for the ideal mating for spectacular wide and sharp "spacewalk" observing.
Life before Paracorr
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 a 0.1 degree diffraction limited field.
Previous attempts to correct for coma have been limited in usefulness. Some correctors were designed mainly for astrophotography. Dedicated coma correcting eyepieces were another approach. However, these were limited to 50 degree apparent fields and would orphan your existing eyepiece collection.
Life with Paracorr
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 color or spherical aberration! You no longer have to constantly shift a Dobsonian to keep objects centered 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.
Paracorr is recommended for use with all Tele Vue eyepieces because our Plýssls, Radians, Panoptics and Naglers achieve higher levels of aberration correction than competitive models. However, Paracorr is also compatible with other eyepiece makes.
Paracorr Eats Coma
The Paracorr can be used with both 2" and 1 1/4" eyepieces, as well as with your 35mm camera body. For visual use, slip Paracorr into your focuser like a Barlow lens, and your eyepiece into Paracorr. 1 1/4" eyepieces will make use of Paracorr's special low profile 1 1/4" reducing adapter. Paracorr is threaded for 2" filters.
Astrophotography
Mount your 35mm SLR to Paracorr, and the quality of full frame photos will be spectacular, since star image sizes on film can be less than .001" over the full frame for an f/4.5 mirror. Edge-of-field sharpness is further enhanced since Paracorr also acts as a field-flattener.
User Reports
"Wow - On our 30" f/4 and 17.5" f/4.5, using 10 different eyepieces, we noted a 75% - 95% reduction in edge field coma. Paracorr is a must for anyone who owns a fast ratio telescope and enjoys wide field, deep sky viewing." - Tom Bemus
"l begun my tests with the first quarter Moon and the 20-inch (f/3.9). Without a coma corrector there was a slight smearing of lunar detail away from the center of the field. It looked like the focus needed to be 'tweaked,' but, of course, doing this did not improve the view. With the Paracorr the entire disk of the Moon appeared in sharp relief." -Sky & Telescope Magazine