Tele Vue Nagler T4 22mm 82° Eyepiece - 2"

The Nagler Type 4 Design

Each Nagler Type 4 features long eye relief along with an 82° apparent field, and new glass technology improved eye relief, contrast, ghost suppression and linearity (freedom from pincushion distortion) for any speed (f/#) telescope while keeping size and weight down.

Tele Vue does not publish the coatings of the Type 4. Its 22mm focal length makes it a low-power eyepiece in most telescopes, for large nebulae such as the Veil and for star fields.

Calculating True Field with the 31.1mm Field Stop

The true field of view you see in the sky is determined not by the apparent field, but by the eyepiece's 31.1mm field stop diameter and your telescope's focal length. To calculate the true field in degrees, use Tele Vue's formula: True Field = (Eyepiece Field Stop ÷ Telescope Focal Length) × 57.3.

For example, in a telescope with a 2000mm focal length, such as an 8" f/10 SCT, the 22mm Nagler delivers a true field of (31.1mm ÷ 2000mm) × 57.3 = 0.89°. That is wider than the full Moon, which spans about 0.5°.

Magnification from f/4.5 to f/14 Telescopes

The 22mm focal length provides low to medium power, ideal for locating objects and observing large-scale structures. The exit pupil, which determines image brightness, is calculated by dividing the eyepiece focal length (22mm) by the telescope's focal ratio. Tele Vue's chart gives 4.9, 4.2, 3.1, 2.2 and 1.6mm at f/4.5, f/5.2, f/7, f/10 and f/14.

• Fast f/4.5 Reflector: Yields a 4.9mm exit pupil, bright views for sweeping nebulae and star clusters.
• Standard f/10 SCT: Produces a 2.2mm exit pupil, for galaxies and planetary nebulae.
• f/14 telescope: Results in a 1.6mm exit pupil, providing higher magnification for resolving detail in globular clusters like the Hercules Cluster (M13).

19mm Eye Relief and the Instadjust Eyeguard System

Eyeglass wearers should look for 15mm to 20mm of eye relief, and this eyepiece has 19mm. Tele Vue's Instadjust eyeguard housing gives maximum eye relief for eyeglass wearers in the down position; pulling it up permits click-stop setting of the eyeguard height.

Without glasses, start with the housing pulled out all the way and keep "clicking down" until you find the most comfortable position where you still see the entire field. The soft rubber eyeguard folds up or down, whichever is more comfortable. The system minimizes extraneous outside light, and the generous eye relief minimizes eye lens fogging from eye moisture in cold weather.

Pairing with Paracorr, Barlows, and Powermates

A Newtonian or Dobsonian shows coma, off-center stars that look like little comets, which no eyepiece removes. The Paracorr Type-2 eliminates it; scopes faster than f/5.0 see the greatest results. Its 1.15x magnification factor makes the 22mm act like a 19mm.

To increase magnification for planetary or double-star observing, a 2x Barlow or Powermate makes the 22mm Nagler T4 act like an 11mm eyepiece, and a 4x Powermate like a 5.5mm.

Nagler 22mm T4 vs. 19mm T7, 31mm T5 and 16mm T5

Comparisons from Tele Vue's chart:

• vs. Nagler 19mm T7: The 19mm Type 7 is also a 2" 82° eyepiece with 19mm of eye relief, with a 27.1mm field stop and a little more power. The 22mm T4's 31.1mm field stop shows more sky.
• vs. Nagler 31mm T5: The 31mm Nagler T5 has a 42.0mm field stop, the largest of the Naglers, and 19mm of eye relief. The 22mm T4 gives more magnification with the same 82° field.
• vs. Nagler 16mm T5: The 16mm T5 has a 22.1mm field stop and 10mm of eye relief and is not Dioptrx ready (N). The 22mm T4 has 19mm of eye relief and is Dioptrx ready (Y).

1.50 lb Construction and DIOPTRX Compatibility

Weighing 1.50 lbs (680 g), the Nagler T4 22mm may need a balance adjustment on a small mount or a light Dobsonian. The weight is enough to extend the eyeguard if you pick the eyepiece up by the black barrel; it cannot fall out of the Instadjust housing. Do not unscrew the chrome barrel, to avoid dust and dirt getting in, or the identifying ring, which keeps the Instadjust housing in place; re-assembly needs a special tool.

This eyepiece accepts DIOPTRX, which attaches and locks onto the top of the eyepiece and corrects astigmatism in place of your glasses. Choose the model that matches your eyeglass prescription for astigmatism, from ¼ to 3½ diopter, and rotate it to your astigmatic axis. It is always completely aligned to the eyepiece optics.