Concept: 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. — Al Nagler
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.
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.