| 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 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.
The Type-4 models feature about long eye relief and with the "instajust" eyeguard are best for eyeglass wearers or Dioptrx users.
