Tele Vue Nagler T7 19mm 82° Eyepiece - 2"

The 82° Spacewalk View with 19mm of Eye Relief

The original 13mm Nagler was the first eyepiece to give well-corrected wide "spacewalk" views with an 82° apparent field. By comparison, Plössls give 50° and Panoptics 68°.

Tele Vue's Type 7 manual says: "If you have been waiting for a Nagler series for eyeglass wearers, the Type 7 is it," combining the 82° field with 19mm of eyeglass-friendly eye relief and a large eyelens.

Calculating True Field: The 27.1mm Field Stop at Work

The true field of view, how much actual sky you see, is determined by the eyepiece's internal field stop, not just its focal length. The Nagler T7 19mm has a 27.1mm field stop, about the 27mm maximum for 1¼" eyepieces; it has a 2" barrel.

To calculate the true field of view (TFOV) in your telescope, use the Tele Vue formula: TFOV = (Eyepiece Field Stop ÷ Telescope Focal Length) x 57.3. For a telescope with a 2000mm focal length, the T7 19mm yields a TFOV of (27.1 ÷ 2000) x 57.3 = 0.78°, room for globular clusters and smaller galaxies.

Exit Pupil Performance: From a 4.2mm Beam at f/4.5 to 1.4mm at f/14

The exit pupil, the beam of light the eyepiece presents to your eye, sets image brightness. Tele Vue's chart gives 4.2, 3.7, 2.7, 1.9 and 1.4mm at f/4.5, f/5.2, f/7, f/10 and f/14.

• Fast f/4.5 Scopes: A 4.2mm exit pupil, for sweeping star fields and large nebulae.
• Mid-Range f/7 Scopes: A 2.7mm exit pupil, for galaxies and planetary nebulae.
• Slow f/10 Scopes: A 1.9mm exit pupil, for brighter objects such as M42 or M13.
• Long f/14 Scopes: A 1.4mm exit pupil, for smaller targets.

Designed for Eyeglasses: 19mm Relief, DIOPTRX, and a Locking Eyeguard

Observers who wear glasses to correct astigmatism should look for 15mm to 20mm of eye relief, and this eyepiece has 19mm. The Type 7 is designed for optimum viewing whether or not you wear eyeglasses.

It is ideal for DIOPTRX, which locks onto the top of the eyepiece and replaces glasses for astigmatism; the chart marks it Dioptrx ready (Y). For observers without glasses, the adjustable, locking eyeguard helps position your eye at the exit pupil and blocks stray light. Pull it fully out, then slide it down while looking through the eyepiece until you just see the full field with your peripheral vision, and note the height on the green indicator lines. The 19mm of eye relief also minimizes eye lens fogging in cold weather.

Paracorr, Barlows and Powermates

Newtonian and Dobsonian telescopes show coma, which no eyepiece removes. The Tele Vue Paracorr Type-2 eliminates it; scopes faster than f/5.0 see the greatest results. Its 1.15x magnification factor makes the 19mm act like a 16.5mm.

To increase magnification, pair it with a Tele Vue Barlow or Powermate. A 2x Powermate effectively transforms it into a 9.5mm eyepiece, while a 4x Powermate provides the view of a 4.75mm eyepiece, for planets on nights of steady seeing.

Nagler T7 19mm vs. Panoptic 19mm: Apparent Field and Eye Relief

Comparisons from Tele Vue's chart:

• Tele Vue Nagler T7 19mm: 82° apparent field, 27.1mm field stop, 19mm of eye relief, 2" barrel, Dioptrx ready (Y).
• Tele Vue Panoptic 19mm: 68° apparent field, 21.3mm field stop, 13mm of eye relief, 1¼" barrel, Dioptrx with adapter (Y*).

Build and Parfocality: A 581g, 2-inch Eyepiece

The Nagler T7 19mm weighs 581 g (1.28 lbs). Nagler Type 7 eyepieces are parfocal with each other when used in 2" mode.

They are also parfocal with most other 1¼" Tele Vue eyepieces when those eyepieces are used in the Tele Vue Hi-Hat 1¼" to 2" adapter (ASF-8125). Do not remove the chrome barrel, to avoid getting dust and dirt into the eyepiece.