Tele Vue Paracorr.

Concept: I have built Newtonian reflectors since my high school days and still have my 12"
f/5.3. Knowing how the Nagler eyepiece complemented fast Dobsonians and Newtonians by
removing eyepiece induced astigmatism, I became intolerant of the inherent defect of coma in
a parabolic mirror.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 colour correction, spherical abberation and convenience in use. Paracorr (parabola
corrector) uses 2 multi-coated, high index doublets, is completely colour-free, center and
edge, and installs like a Barlow. Coma is corrected so well, the diffraction limited field area of
an f/4.5 is increased 36 times! - Al Nagler

An optical chain is as good as its weakest link. With the development of the 82º 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
flat-field and sharpness.

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 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 are limited to visual use and 50 degree apparent fields and orphan
your existing eyepiece collection.

Life with Paracorr
Paracorr is a universal corrector that tightens and intensifies starimages 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 Plossls, Wide
Fields, Panoptics, and Naglers achieve higher levels of lateral color and astigmatism
correction than competitive models. However, Paracorr is also compatible with other eyepiece
makes.

Easy to use
Paracor drops into your forcuser like a Barlow lens. With only a slight 1.15x magnifying
factor,
an f/4.5 telescope becomes an f/5.17. Paracorr requires about 1/2" in-travel from your current
focus location. Paracorr is threaded for 48mm filters and has a captive lock-screw for
convenience.

Mount a T-ring to your 35mm camera and attach it to Paracorr's lens assembly. Slip it into
your focuser and you're set for coma-free photography.

Paracorr Eats Coma
The 2" Paracorr can be used with both 2" and 1 1/4" eyepieces, and your 35mm camera
body. For visual use, slip Paracorr into your focuser and your eyepiece into Paracorr. 1 1/4"
eyepieces will make use of Paracorr's special low profile 1 1/4" reducing adapter.

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.

Try Paracorr on your "DobNewt." We think you'll agree that the revolution is complete.

Prices:
PVL-2008 - Paracorr VISUAL - £223.00
PLA-2001 - Paracorr Photo Lens - £154.00
PTT-2002 - Tunable Top - £43.00
PSB-1100 - Paracorr to SBIG 11000 - £182.00

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, deepsky viewing." - Tom Bemus, Martz Observatory, Frewsburg, NY

"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,
Sept. '91


OPTIMIZING YOUR TELE VUE NAGLER TYPE 4 AND TYPE 5 EYEPIECES WHEN USING
PARACORR
As you've read, all Newtonian/Dobsonian telescopes can benefit from using a Tele Vue
Paracorr (Parabola Corrector) to eliminate coma in the image. One aspect to optimizing this
correction is the distance of the eyepieces focus point (field stop location) to the last surface
of the Paracorr lens (within a small +/- tolerance of course).

The length of the standard Paracorr eyepiece barrel has accommodated all Tele Vue
eyepieces, up to the introduction of the Nagler Type 4s and 5. While these eyepieces will
work with the standard Paracorr eyepiece barrel, its length is just too long for optimum coma
correction. Make no mistake about it. A Newtonian owner is still far better off using the
standard Paracorr than no Paracorr at all.

But, in true Tele Vue fashion, when we saw the opportunity to tweak the coma correction of
the Paracorr/Nagler Type 4 and 5 relationship, we just couldnt pass it up. Simply creating a
1/2 shorter length eyepiece barrel to space the eyepiece closer to the Paracorr lenses was
all
that was necessary. For your reference, here is a recommendation guide for choosing the
best setup for various Tele Vue eyepieces to get optimum correction:

STANDARD LENGTH PARACORR BARREL USED IN 2" MODE: 20mm Nagler Type 2,
13mm Nagler, 35mm Panoptic, 27mm Panoptic, 22mm Panoptic

STANDARD LENGTH PARACORR BARREL USED WITH 1.25" ADAPTER: All Radians, All
Plossls, 4.8mm and 7mm Naglers, 15mm and 19mm Panoptics, Tele Vue Zoom 8-24mm

SHORTER LENGTH PARACORR BARREL USED IN 2" MODE: 31mm Nagler Type 5, 22mm
Nagler Type 4, 17mm Nagler Type 4

SHORTER LENGTH PARACORR BARREL USED WITH 1.25" ADAPTER: 16mm Nagler
Type
2, 12mm Nagler Type 2, 12mm Nagler Type 4, 9mm Nagler

CAUTION: Do NOT use Barlow lenses with the shorter barrel; the Barlow may contact the
Paracorr lens.

Since every Tele Vue eyepiece already incorporates superior design, construction and 100%
Q.C. (each eyepiece is checked at f/4), you can now be sure that they will also perform with
your Paracorr-equipped Dob/Newt even better than you imagined.

The Astronomy Shop

1 Tone Hill. Wellington

Somerset TA21 0AU

United Kingdom

Telephone: +44 (0)1823 665510