The Paracorr Type-2 coma corrector from Tele Vue significantly enlarges the coma-limited field of pinpoint sharpness in reflector telescopes. With the Paracorr, you'll no longer have to invest in dedicated, costly coma-corrected eyepieces; get yourself some basic, quality Plössls and enjoy.
If you have an f/4.5 or slower telescope and are thinking that a faster scope may be in your future, the Paracorr Type 2 will work at least as well as the original Paracorr in your current scope. The Paracorr Type-2 tightens and intensifies star images on any reflector telescope with f-ratios faster than f/4.5, without adding any chromatic or spherical aberrations. You'll get nearly the same area of tight star points across an eyepiece's field of view as with Tele Vue's premium apochromatic refractors.
Paracorr's Type-2 model slips into 2" focusers just like a Barlow lens, and comes with the ACF-2125 2" to 1.25" reducer so that it accepts any 2" & 1.25" eyepieces. To minimize the necessary in-travel upon your focuser due to some additional length, a mild 15% Barlow effect is designed into the Paracorr to effectively push the focus out.
The Paracorr's Type-2 "Tunable Top", by simply loosening a screw and rotating the Tunable Top, permits you to observe through all of Tele Vue's eyepieces and many other eyepieces with fully-optimized aberration control. The top's settings raise and lower the eyepiece barrel height, allowing a perfect field-stop-to-Paracorr-lens distance (which varies based on eyepiece design). The Paracorr Type-2 allows separating the optical assembly from the Tunable Top and using it with Tele Vue imaging system components to permit use with SLR and CCD cameras. APS size formats 27mm diameter are recommended to minimize field vignetting. It is ideal for mirrors as fast as f/3.
Newtonian reflectors (whether Dobsonian style or a conventional mount with tripod) are great at gathering lots of light at a low price, but suffer from coma distortion. Only the central ~25% or so of the field of view is pinpoint sharp, so there's a lot of fussing around with scope position to enjoy extended observing with reflectors. It is the economical compromise that many make in order to enjoy the larger apertures reflectors afford; we can't all have 5" apochromatic refractors. Tele Vue's Paracorr Type-2 is the answer.