Astigmatism and field curvature are 2 factors that most influence the off axis sharpness especially in “fast” objectives (below f/6). Eyepiece designers had tried for many years to eliminate these aberrations but it was not until the 1980s that a breaktrough occurred – the Nagler eyepiece.
Since then Al Nagler has refined this series of eyepieces taking advantage of different exotic glasses and improved coatings to deliver quite simply the best performance you can get out of an eyepiece.
Nagler Type 6
The 7-element, Nagler Type 6 design is based on the original patented Nagler design. This new 7-element design update for the short focal length Nagler deserves its own designation. Using different exotic materials, coating processes and design ingenuity, Al has massaged more eye-relief, contrast, and true field of view into the shorter focal length Naglers, while maintaining the absolute sharpness of the originals. Eye-relief is 12mm on each model, and all are sized about the same as the original 7mm! Weight about 0.4 to 0.5 lbs.
Concept: The goal we set designing these new eyepieces was to increase contrast, maintain or increase eye-relief, reduce size and weight, and maintain the sharpness of the originals. They are all parfocal and great with the Bino Vue.