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Televue ATT-2125 Paracorr Tunable Top for Televue BIG Paracorr

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Televue ATT-2125 Paracorr Tunable Top for Televue BIG Paracorr - including 1.25" Adapter


The 2” Tunable Top with 1¼” Adapter (model #ATT-2125) is the tunable top from the standard Tele Vue 2” Paracorr Type-2. It permits positioning all eyepieces for optimum coma correction. For use on the BIG Paracorr Type-2, the “VISA” (Visual / Imaging System Adapter), is required. A 3” Tunable Top is not required since secondary mirror size limits maximum exit pupil diameter to around 7mm. Therefore, the widest true field eyepiece choice with an f/3 (f/3.45 when used with Paracorr) is Tele Vue’s own 21mm Ethos, which delivers a 6.1mm exit pupil at f/3.45.


Attach the Tunable Top by unscrewing the Stop Flange from the top of the BIG Paracorr Type-2 and replacing it with the “VISA” adapter. Then screw on the Tunable Top. Tighten the Tunable Top snuggly.


For 2” Eyepieces

1) Make sure eyepiece lock screws (A) are loosened
2) Remove 1¼” adapter.
3) Slip 2” eyepiece into the Paracorr
4) Tighten eyepiece lock screws (A)
5) To adjust for eyepiece position,
a. Slightly loosen the height adjustment lock knob (B) that clamps on the slot.
b. Push the screw (B) to adjust the height of the eyepiece, following the guidelines in the eyepiece position chart below.
c. Tighten the height adjustment lock knob (B).

For 1.25” Eyepieces

1) Slip the 2” to 1¼” reducing adapter into the Tunable Top and tighten lock screws (A).
2) Place the eyepiece in the adapter and tighten the lock screw (C)
3) Follow the adjustment procedures outlined above in step 4.

Note: Focus the telescope after properly setting the eyepiece position. Do not accidentally use the tuning feature for focussing.
The easiest method for finding optimal correction for other brand eyepieces is to first establish the focus position with a Tele Vue eyepiece at its known Paracorr setting. Then insert your other eyepiece and use the tunable top until focus has been reached. Note the mark on the Paracorr body for the setting. Use your telescope focuser to tweak the focus if necessary.

CAUTION: Do not insert any accessory (Barlows, collimators, etc.) with a barrel length more than 1¾” into the Paracorr, to avoid contact with the Paracorr lens.

From Our Blog
  • BIG Paracorr User Profile: Jay Butler
    Jay says the BIG Paracorr Type-2 "gives me nice round stars without vignetting all the way out to the corners of my camera's KAF-16200 CCD. And whatever the seeing, the Big Paracorr gives me sharper and deeper images than I have ever been able to attain with other high-end equipment combinations."
BIG Paracorr Type-2 Product Introduction Video from Sky & Telescope




Optimizing the Coma Correction by Using Paracorr's Tunable Top

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). Typical eyepieces used with fast Newtonians can have field stop locations differing by as much as half an inch. To accommodate for the differences, we developed the "Tunable Top."

The "Tunable Top" permits optimized aberration control for all Tele Vue eyepieces and many others, by simply loosening a screw and rotating the Tunable Top. The eyepiece barrel height raises and lowers, allowing you to maintain the proper field stop to Paracorr lens distance. For your reference, here is a recommendation guide for choosing the best setup for various Tele Vue eyepieces to get optimum correction:

Table for 3" BIG & 2" Paracorr Type-2 (VIP-3010/2010)
(Please note, to be able to attach the ATT-2125 Paracorr Tunable Top to the BIG Paracorr, you would also need a AVI-3200 visual imaging system adapter (VISA) as well.)
Position A B C D E F G H
2" Oculars
(Dist. from Ref.)
-0.4" -0.3" -0.2" -0.1" 0" +0.1" +0.2" +0.3"
Panoptic             35 41 & 27
Nagler Type 4   22       17    
Nagler Type 5 31         26 20  
Nagler Type 6                
Nagler Zooms                
Ethos 21 & 17             13, 10,
3.7SX & 4.7SX
(w/2" adapt.)
1¼" Oculars
(Dist. from Ref.)
0" +0.1" +0.2" +0.3" +0.4" +0.5" +0.6" +0.7"
    32-to-8       40
Radian       all        
DeLite       all        
Panoptic       24 & 19        
Delos 17.3 & 14     12-to-3.5
17.3* & 14*
Nagler Type 4       12        
Nagler Type 5       16        
Nagler Type 6       all        
Nagler Zooms       2-4 & 3-6        
Ethos   8 & 6   3.7SX & 4.7SX        
*Use at "D" with AIT-2125 In-Travel Adapter.
All eyepiece interfa...
All eyepiece interfaces have non-marring brass clamp rings.


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