The Nagler eyepiece was revolutionary as the first eyepiece to deliver breath taking wide fields of view while still providing sharp images from edge to edge. In contrast to the objective of your telescope which rarely covers an image angle of more than 2°, Nagler eyepieces remain sharp over an angle of 82° to truly inspire a spacewalk vista. For this reason extreme care must be taken to correct for aberrations – especially away from the optical axis.
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. While other manufacturers may boast impressive field sizes, Tele Vue’s philosophy of inspiring spacewalk vistas always keeps their optical devices well ahead of the pack.
Nagler Type 5
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.
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, 26, 20, 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), while the shorter focal length Type-6 models 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.