Because the original 1989 TeleVue Paracorr (Para
ector) eliminated the coma inherent in fast parabolic mirrors, it made reflectors with "fast" f/4.5-class focal ratios and longer as aberration-free as "slow" f/12 scopes. However, with more compact "no ladder" Dobsonians with focal ratios in the f/3 range becoming ever more popular, it became apparent that something even better than the original Paracorr was needed to keep up with the dropping focal ratios. Just as the original Paracorr was optimized for f/4.5 mirrors, a new Paracorr was needed that was optimized for f/3.
The new TeleVue Paracorr Type 2 is that new Paracorr. Developed in 2010 after extensive design work and testing, the TeleVue Paracorr Type 2 can make an f/3 mirror act like an f/12 without a Paracorr. With essentially diffraction-limited images across the entire field, the Paracorr Type 2 makes the new breed of f/3-class “ladder-less” Dobs possible, particularly with very wide field eyepieces, and superior in terms of convenience, field-of-view, and optical perfection when using top-quality mirrors.
The Paracorr Type 2 coma corrector fits into the 2” focusers of all Newtonian reflectors and Dobsonians. It holds 2” eyepieces directly and has an adapter for 1.25” eyepieces. The Paracorr is ideal for premium wide field eyepieces like the 100° to 110° field TeleVue Ethos and 82° field Naglers, but all quality eyepieces will benefit. It has a “tunable top” that allows you to optimize the Paracorr’s coma correction by precisely setting the distance from the eyepiece focus point (the field stop location) to the last surface of the Paracorr lens (within a small +/- tolerance, of course).
The typical wide field eyepieces used with fast Newtonians can have field stop locations differing by as much as half an inch. The “tunable top” permits optimizing this critical spacing for all TeleVue eyepieces, and many others, by simply loosening a hand-tighten knob in the side of the Paracorr Type 2 and rotating the tunable top. This raises and lowers the eyepiece in relation to the Paracorr optics, allowing you to set the proper eyepiece field stop to Paracorr lens distance.
As can be seen in the image above, the tunable top adjustment slot in the Paracorr barrel is marked at eight specific intervals to match the spacing requirements of various TeleVue eyepieces so you can quickly dial in the proper spacing as you change between eyepieces. A chart with the correct spacing marks for the various TeleVue eyepieces (even the 31mm Nagler and 21mm Ethos is provided with the Paracorr Type 2 to eliminate guesswork. For your reference, TeleVue’s recommendation guide for choosing the best tunable top height setting for various TeleVue eyepieces to get optimum coma correction with the Paracorr Type 2.
The design of the Paracorr Type 2 allows you to separate the optical assembly from the tunable top and use it with TeleVue imaging system components for imaging with 35mm, DSLR, and CCD cameras. APS-C size format cameras with an approximately 27mm sensor diagonal measurement are recommended to minimize field vignetting. The TeleVue Paracorr Type 2 increases the magnification by 1.15x.