TeleVue Ethos 6mm 100° Eyepiece - 1.25"/2"

The 100° Field and 10.4mm Field Stop

At high power, a wide apparent field gives a wide true field for the magnification and extends the time an object drifts across the view before the telescope needs to be nudged. The 6mm Ethos offers a 100° apparent field for high-magnification views of planets, double stars and small planetary nebulae.

The true field of view is determined by the eyepiece's 10.4mm field stop diameter and your telescope's focal length. In the Tele Vue NP101is (540mm focal length), Tele Vue's table gives 90x and a true field of 1.10° (10.4 / 540 x 57.3), wide enough to frame the entire Dumbbell Nebula (M27) with sky around it.

The Dual 1¼"/2" Barrel

The Ethos 6mm features a dual-purpose barrel that fits both 1.25" and 2" focusers and diagonals, offering convenience rather than an optical advantage in 2" mode. The 1.25" barrel is threaded for standard 1.25" filters, allowing you to enhance contrast on planetary or nebular targets directly at the eyepiece.

In 1¼" holders, a lock screw on the eyepiece's 2" section can be tightened against the outside of the holder; the eyepiece is heavy and can fall out of slip-fit holders unless the lock screw is used. In 2" holders, remove the eyepiece lock screw and keep the holder's screw out of the barrel slot. To use 48mm (2") filters, the Tele Vue EBX-2120 barrel extender can be added, which also helps in parfocalizing eyepiece sets.

15mm Eye Relief for High-Power Viewing

The Ethos 6mm has 15mm of eye relief, the same as every Ethos and Ethos-SX in Tele Vue's chart, so the viewing position stays familiar as you change focal length. The chart also marks it Dioptrx ready.

With small exit pupils such as 1mm or less, you probably will not need eyeglasses. The 6mm Ethos gives a 0.6mm exit pupil at f/10 and 1.3mm at f/4.5 (per the chart). If you do wear glasses for astigmatism, choose eyepieces with 15mm to 20mm of eye relief, or a Dioptrx in place of the glasses.

Parfocality with the 8mm Ethos

The 6mm and 8mm Ethos eyepieces are designed to be parfocal, meaning you can switch between them with little to no refocusing required.

When used in a 2" focuser, the 6mm Ethos will typically reach focus about 0.75 inches further out than a 26mm Nagler Type 5 eyepiece. In a 1.25" focuser with Tele Vue's "high-hat" adapter, it becomes parfocal with the entire line of Tele Vue Plössls, Type 6 Naglers, and 1.25" Panoptics, and Nagler Zooms.

Optimizing for f/5.5 or Faster Newtonians

Fast Newtonian and Dobsonian reflectors show coma, which makes off-centre stars look like little comets, and a 100° field shows it clearly. Use the Paracorr Type-2 coma corrector for any reflector with a focal ratio of f/5.5 or faster.

The Paracorr Type-2 inserts into your 2" focuser and eliminates the mirror coma, for the same kind of full-field sharpness Tele Vue's NP-Series refractors show. It also acts as a 1.15x magnification amplifier, effectively turning an f/4.5 scope into an f/5.2 system.

Ethos 6mm vs. Delos 6mm: A Choice of Immersion or Eye Relief

Tele Vue makes a 6mm in both the Ethos and Delos lines. The choice between the Ethos and Delos lines comes down to a trade-off between the apparent field of view and eye relief.

• Ethos 6mm: With a 100° apparent field and 15mm of eye relief, and a 10.4mm field stop, the Ethos gives the wider view.
• Delos 6mm: The Delos has a 72° apparent field and a 7.6mm field stop with 20mm of eye relief, which suits observers who must wear eyeglasses.

Achieving Higher Powers with Barlows & Powermates

On steady nights, or with short focal length telescopes, you can increase the magnification of the 6mm Ethos while retaining its 100° field by using a Tele Vue Barlow or Powermate. They are the recommended route to higher magnifications with a 100° field.

When pairing the Ethos with a 2" Powermate, you should use the eyepiece's native 2" barrel for a secure fit. A 2x Powermate transforms the 6mm into a 3mm eyepiece, for splitting tight double stars or examining lunar craterlets. Note that a 1.25" filter should not be threaded into the Ethos when used with a 2x Powermate, as it may contact the Powermate's top lens element.