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This is a used Tele Vue 31mm Nagler that is in excellent condition. The optics are clean with only some slight amount of dust from normal use. Obviously, this will not affect your views.
This comes with both dust caps, but no box.
Take a "spacewalk" across a wide, sharp 82° apparent field
Compare a penny to a half dollar to see the relative size between a 50° and 82° apparent field - almost 3 times the area difference! And while others boast of impressive apparent field sizes, Tele Vue's philosophy of "showing no field unless it's fine" stresses full field image quality as the ingredient for impressive views. Blackened lens edges, anti-reflection threads and rubber eyeguards deliver maximum contrast. Adapter skirts for 2" focusers on larger 1¼" models and rubber grip rings are additional Tele Vue "firsts". Even 2"/1¼" barrel models have an additional feature allowing the 2" extension tube (EBX-2120) to be screwed on, which permits use of 2" filters as well as 1¼". 100% full field visual inspection on our own flat-field test instruments guarantees the performance of every Tele Vue eyepiece.
With the 31mm, the unique 6-element design using four exotic glasses, maintains the contrast advancement of the Type 4s while achieving a true field area 82% larger than the 22mm Type 4! Owners of fast Dobsonian/Newtonians can enjoy a larger true field, free of secondary shadowing, than ever before. For example, a 12.5", f/4.5 scope with a Paracorr will deliver a 1.5 degree field (3 Moon diameters), at 53x with a 6mm exit pupil. Use our eyepiece calculator to figure out what the 31mm will deliver on your scope.
Why Are There 3 Types of Naglers?
To achieve the full magnification range over 82° apparent field of view requires two types: Nagler Type-5 with focal lengths of 31, 16mm and Nagler Type-6 with focal lengths of 13, 11, 9, 7, 5, 3.5, 2.5mm.
The Type-5 permits the largest true field possible (31mm has 42mm field stop).
Type-6 models have shorter focal lengths, are parfocal, with similiar size and weight, and all with a comfortable 12mm eye relief.
The Type-4 models feature about 18mm of eye relief and with the "instajust" eyeguard are best for eyeglass wearers or Dioptrx users in their 22, 17, 12mm focal length range.
Al Nagler said of the Nagler line, "You may know there's a long history of naming eyepieces after their designers: Kellner, Erfle and Plossl, to name a few. In the late 70's I designed an eyepiece sufficiently radical that I dared attach my name to it. Even today, I must admit a little discomfort when talking about 'Nagler' eyepieces.
"With 'Naglers', my aim is to approach the wide angle perspective of naked eye vision, while maintaining the highest degree of sharpness, contrast, and viewing comfort. The goal is to allow the telescope to virtually 'disappear,' leaving the impact of 'spacewalk' viewing."
| Model # | EN5-31.0 |
| Focal Length (mm) | 31 |
| Barrel Size (in.) | 2" |
| Apparent Field of View (deg.) | 82 |
| Eye Relief (mm) | 19 |
| Weight (lb / oz) | 2.20 / 35.2 |
| Field Stop (mm) | 42 |