| 31-mm | |
| Model # | EN5-31.0 |
| Focal Length (mm) | 31 |
| Barrel Size (in.) | 2" |
| Apparent Field (deg.) | 82 |
| Eye Relief (mm) | 19 |
| Weight (lb / oz) | 2.20 / 35.2 |
| Field Stop (mm) | 42 |
| Compare to similar focal lengths | |
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.
To achieve various features requires different design tradeoffs and thus the different types of Nagler eyepieces. The largest possible true fields of view for an 82°' apparent field of view in both 2" and 1¼" formats are achieved with the Nagler Type 5 series, with focal lengths of 31 and 16 mm
Compact size in medium to short focal lengths is achieved with the Nagler Type 6, available in focal lengths of 13, 11, 9, 7, 5, and 3.5 mm.
To achieve eyeglass friendly eye relief without excessively large and heavy designs requires the other two Nagler types. The 22mm Type 4 and 19, 14, 9, 5.5 mm Type 7 with their long eye relief feature adjustable height eyeguards and are best for eyeglass wearers or Dioptrx™ users.
