When Tele Vue designed the Radian series of eyepieces, Tele Vue used the Nagler concept as the basis. However with the Radians, Tele Vue decided to balance size, weight, and cost relative to a consistent 20mm eyerelief. During the design process Tele Vue found that we could not only balance these factors for 1.25" focussers, but improved glass types lead to better imaging, contrast enhancement, reduced pincushion, ghost suppression, and a newer concept in a click-stop adjustable eyeguard as well.
Applying that experience to the 82 degree, Nagler Type 2 design goals, would potentially provide increased eye-relief, more contrast, reduced pincushion and more true field as well.
The first Nagler Type 4 to arrive is the 12mm version, replacing not only the 12mm Nagler Type 2 but its predecessor 13mm (my first Nagler) and the 11mm, now considered a collector item. Users confirm that for deep sky viewing, the comfort, clarity and contrast of the 12mm Type 4 gets us closer to our "spacewalk" viewing goal. Similar in size and weight to Type 2, it has more true field and 50% greater eye relief, while using just six elements.
As compared to the 20mm Nagler Type 2, the 22mm Nagler Type 4 weighs just 1.5 lbs, has an eye-relief of 19mm, and has almost 30% more true field area. With these impressive specs the 22mm Nagler Type 4 is worth looking into (pun intended). Let's spacewalk!