Tele Vue Nagler T6 13mm 82° Eyepiece - 1.25"

The 82° Nagler "Spacewalk" Experience

The original 13mm Nagler was the first eyepiece to give well-corrected wide "spacewalk" views with an 82° apparent field. By comparison, Plössls have 50° and Panoptics 68°. A wider apparent field keeps a target in view longer in a telescope without a drive, such as a Dobsonian.

The 13mm Type 6 has 7 lens elements; no further details on its correction are published.

Framing the Sky: Calculating True Field with a 17.6mm Field Stop

An eyepiece's true field of view, how much actual sky it shows, is determined by its internal field stop diameter and the telescope's focal length, not just its apparent field. The Nagler T6 13mm has a 17.6mm field stop. You can calculate the true field for your 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, the Nagler T6 13mm provides a true field of 0.84°, room for the bright core of the Lagoon Nebula (M8), though the whole nebula is wider.

Performance at f/4.5 to f/14: Exit Pupils from 2.9mm to 0.9mm

The exit pupil, calculated as Eyepiece Focal Length ÷ Telescope f-ratio, determines the brightness of the background sky and the image scale. Tele Vue's chart gives 2.9, 2.5, 1.9, 1.3 and 0.9mm at f/4.5, f/5.2, f/7, f/10 and f/14. A larger exit pupil gives a brighter image; a smaller one darkens the sky background.

• At f/4.5 (Fast Dobsonian): A 2.9mm exit pupil, for galaxies and nebulae.
• At f/7 (Apochromatic Refractor): A 1.9mm exit pupil, for globular clusters such as M13.
• At f/10 (Schmidt-Cassegrain): A 1.3mm exit pupil, a medium-high power for Jupiter and Saturn.
• At f/14 (Maksutov-Cassegrain): A 0.9mm exit pupil, for double stars.

Ergonomics: The 12mm Eye Relief and Dioptrx Astigmatism Correction

The Nagler T6 13mm features 12mm of eye relief. For observers who wear glasses to correct astigmatism, 15mm to 20mm is recommended, so with glasses you may lose some of the field (vignetting). Without glasses, 12mm works for most observers.

For those with astigmatism, Tele Vue offers the Dioptrx system as an alternative to wearing glasses at the eyepiece. The Nagler T6 13mm 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.

A 1¼" Barrel and 0.40 lbs

Every Nagler Type 6 in Tele Vue's chart has a 1¼" barrel, so the 13mm fits any 1¼" focuser or diagonal. It weighs 0.40 lbs (6.4 oz).

Its barrel takes 1¼" filters (M28.5 x 0.6).

Nagler 13mm T6 vs. Sibling Eyepieces: Field Stop and Eye Relief

Comparisons from Tele Vue's chart:

• vs. Tele Vue 10mm Ethos (17.7mm Field Stop): The 10mm Ethos shows nearly the same true field across a 100° apparent field, at more magnification, with 15mm of eye relief and Dioptrx readiness (Y).
• vs. Tele Vue 14mm Delos (17.3mm Field Stop): The 14mm Delos shows a slightly smaller true field across a 72° apparent field, with 20mm of eye relief and Dioptrx readiness (Y), for eyeglass wearers. The Nagler has the wider apparent field.
• vs. Tele Vue 9mm Nagler T6 (12.4mm Field Stop): The 9mm Nagler T6 is the next step down in field stop, with the same 12mm of eye relief and 82° field.

For Fast Newtonians: Coma Correction with Paracorr Type-2

Newtonian and Dobsonian telescopes show coma, which makes off-center stars look like little comets, more so toward the edge of the field. No eyepiece removes it.

The Tele Vue Paracorr Type-2 eliminates it; scopes faster than f/5.0 see the greatest results. It goes into a 2" focuser like a Barlow and has a 1.15x magnification factor, so an f/4.5 scope works at f/5.2.

System Integration: Reaching Higher Powers with Barlows & Powermates

Tele Vue makes Barlows and Powermates in 2x, 2.5x, 3x, 4x and 5x to raise the power of an eyepiece you already own.

Using a 2x Barlow effectively turns the 13mm Nagler into a 6.5mm eyepiece, doubling the magnification. Al Nagler's guide calls the Powermate an improvement to the Barlow-type design; a 4x Powermate makes the 13mm act like a 3.25mm.

Accessory Ecosystem: BandMate Filters, Dioptrx, and FoneMate

Tele Vue accessories for the Nagler T6 13mm:

• BandMate Filters: The 1¼" barrel takes Tele Vue's 1¼" BandMate Nebustar, O-III and H-Beta filters, which pass select wavelengths and darken the sky so nebulae "pop out".
• Dioptrx Compatibility: As noted, the eyepiece is compatible with Dioptrx astigmatism correctors when used with the required DEA/DNA adapter.
• FoneMate Smart Phone Adapter: For still, video or timelapse images through the eyepiece. Like Dioptrx, the FoneMate needs the DEA / DNA adapter on this eyepiece.

Build and Warranty: A 0.40 lb Eyepiece with Lifetime Protection

The Tele Vue Nagler T6 13mm weighs 0.40 lbs (6.4 oz) and has 7 lens elements.

Every Tele Vue eyepiece, including the Nagler T6 13mm, is covered by a Lifetime Limited Warranty. This commitment protects against defects in material or workmanship, for as long as you own it.