Tele Vue Nagler T6 5mm 82° Eyepiece - 1.25"

The 5mm Nagler T6: A High-Magnification 82° Spacewalk

The original 13mm Nagler was the first eyepiece to give well-corrected wide "spacewalk" views with an 82° apparent field. The 5mm Type 6 brings that field to high power, with 7 lens elements in a 1¼" body 81mm (3.2 in) tall.

Tele Vue does not publish glass types, coatings or correction details for this model.

The 82° Field: Calculating True Field with a 7.0mm Field Stop

The defining feature of any Nagler eyepiece is its 82° apparent field of view (AFOV). At high power a wide field lets a planet drift longer before you nudge the telescope, which helps on a mount without a drive.

While AFOV describes the immersive feel, the true field of view (TFoV), the actual patch of sky you see, is determined by the eyepiece's 7.0mm field stop and your telescope's focal length. You can calculate it with the formula: True Field (°) = (Eyepiece Field Stop ÷ Telescope Focal Length) x 57.3. For example, in a telescope with a 1200mm focal length, the 5mm Nagler T6 yields a TFoV of (7.0mm / 1200mm) x 57.3 = 0.33°, room for the small Ring Nebula (M57) at 240x.

High-Power Observing: Exit Pupils from 1.1mm Down to 0.4mm

The 5mm Nagler T6 is for nights of good seeing. The exit pupil, the beam of light leaving the eyepiece, is small at this focal length, which darkens the sky background.

The exit pupil depends on your telescope's focal ratio (Exit Pupil = 5mm / f-ratio). Tele Vue's chart gives 1.1, 1.0, 0.7, 0.5 and 0.4mm at f/4.5, f/5.2, f/7, f/10 and f/14:

• At f/4.5 (1.1mm exit pupil): For globular clusters in fast Dobsonians.
• At f/7 (0.7mm exit pupil): For small planetary nebulae and planets in refractors.
• At f/10 (0.5mm exit pupil): A very high power for the Moon and planets in Schmidt-Cassegrains, on steady nights; avoid going below 0.5mm in reflectors.
• At f/14 (0.4mm exit pupil): For close double stars in long-focus telescopes, when the seeing allows.

Ergonomics and System Fit: 12mm Eye Relief and Dioptrx Compatibility

Every Nagler Type 6 has 12mm of eye relief. Observers who wear glasses to correct astigmatism should look for 15mm to 20mm, but with exit pupils of 1mm or less you probably will not need eyeglasses.

For observers with astigmatism, this eyepiece is a designated "Y*" model in Tele Vue's system, meaning it accepts a DIOPTRX astigmatism corrector with the addition of a Tele Vue DEA/DNA adapter. The adapter converts the small eyeguard to a larger one so DIOPTRX and FoneMate can be installed. 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

Two Tele Vue accessories change how the 5mm works in a given telescope:

• Paracorr Type 2: Newtonians show coma, which no eyepiece removes. The Tele Vue Paracorr Type 2 eliminates it, and scopes faster than f/5.0 see the greatest results. It has a 1.15x magnification factor, so an f/4.5 scope works at f/5.2.
• Barlows and Powermates: For nights of exceptional seeing or with shorter focal length telescopes, the 5mm Nagler T6 can be paired with Tele Vue's image amplifiers. A 2x Powermate makes the 5mm act like a 2.5mm eyepiece, a power few nights support.

Nagler 5mm T6 vs. The Alternatives: Delos 4.5mm and Sibling Naglers

Comparisons from Tele Vue's chart:

• vs. Delos 4.5mm: The Delos 4.5mm has a 72° apparent field, a 5.6mm field stop and 20mm of eye relief, and is Dioptrx ready (Y), which suits eyeglass wearers. The Nagler has the wider 82° field and the larger 7.0mm field stop.
• vs. Nagler T6 7mm: The 7mm (9.7mm field stop) is easier to use on average nights. The 5mm gives 40% more magnification when the seeing supports it.
• vs. Nagler T6 3.5mm: The 3.5mm (4.8mm field stop) gives 1.4x more power again, which needs very steady air in most telescopes.