Tele Vue Nagler T6 9mm 82° Eyepiece - 1.25"

The 82° Spacewalk Experience in a 1.25" Barrel

Al Nagler's guide gives Naglers an 82° apparent field, against 50° for Plössls and 68° for Panoptics; observers call the view a spacewalk. The Nagler T6 9mm has a 1¼" barrel, so it fits any 1¼" focuser or diagonal.

It stands 3.2 inches (81.3mm) tall with a 48.3mm maximum diameter.

Seven Elements in Four Groups

The Nagler T6 9mm has 7 elements in 4 groups. The glass types, coatings and correction details for this model are not published.

Calculating True Field: The 12.4mm Field Stop

The true field of view, the actual circle of sky you see, is determined by the eyepiece's internal field stop diameter and your telescope's focal length. The Nagler T6 9mm has a 12.4mm field stop. You can calculate the true field for your specific telescope using Tele Vue's formula: True Field = (Eyepiece Field Stop ÷ Telescope Focal Length) x 57.3.

For example, in a telescope with a 1200mm focal length (like an 8" f/6 Dobsonian), the Nagler T6 9mm delivers a true field of (12.4mm ÷ 1200mm) x 57.3 ≈ 0.59°. That holds the globular cluster M13 at 133x, enough to resolve many of its stars.

High-Power Observing: Exit Pupils from 2.0mm to 0.6mm

Tele Vue's chart gives 2.0, 1.7, 1.3, 0.9 and 0.6mm at f/4.5, f/5.2, f/7, f/10 and f/14.

• f/4.5 Telescope: A 2.0mm exit pupil, for globular clusters and brighter nebulae.
• f/7 Telescope: A 1.3mm exit pupil, for planetary nebulae and small galaxies.
• f/10 Telescope: A 0.9mm exit pupil, for Jupiter, Saturn and the Moon.
• f/14 Telescope: A 0.6mm exit pupil, for double stars on steady nights.

The 12mm Eye Relief Trade-Off and Dioptrx Correction

The Nagler T6 9mm has 12mm of eye relief, which works for most observers without glasses. Observers who wear glasses to correct astigmatism should look for 15mm to 20mm, so with glasses you may lose some of the field.

For observers with astigmatism, Tele Vue offers the DIOPTRX Astigmatism Corrector. The Nagler T6 9mm needs a DEA / DNA adapter for DIOPTRX (Y* in the chart); the adapter converts its small eyeguard to a larger one. These eyepieces have shorter eye relief than others recommended for DIOPTRX, so they are best used with it for deep-sky viewing, where your eye pupil is large.

Paracorr, Barlows and Powermates

Newtonians show coma, off-center stars that look like little comets, 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 9mm act like a 7.8mm.

You can also increase the magnification of the 9mm by pairing it with a Tele Vue Barlow or Powermate. A 2x Powermate, for example, would effectively turn the 9mm into a 4.5mm eyepiece, a high planetary power.

Nagler T6 9mm vs. Delos 10mm and Nagler T7 9mm

Comparisons from Tele Vue's chart:

• vs. Delos 10mm: The Delos has a 72° apparent field, a 12.7mm field stop and 20mm of eye relief, and is Dioptrx ready (Y), which suits eyeglass wearers. The Nagler T6 9mm has the wider 82° field and 12mm of eye relief.
• vs. Nagler T7 9mm: The Nagler Type 7 9mm also has an 82° field, with a 13.0mm field stop, 19mm of eye relief and Dioptrx readiness (Y). The Type 6 has 12mm of eye relief and a 12.4mm field stop.

Building a Set: Al Nagler's Field-Stop Increment Method

Choose low and medium power eyepieces in ratios of field stop diameter, such as 1.4 or 2.0, and higher power eyepieces in ratios of magnification. The Nagler T6 9mm has a 12.4mm field stop.

The 13mm Nagler T6 (17.6mm field stop) is a 1.4 step wider. Going up in power, the 7mm Nagler T6 gives 1.3x the magnification and the 5mm 1.8x.