TeleVue Ethos 21mm - 100° 2" Eyepiece

TeleVue Ethos 21mm: 100° 2" Eyepiece: Ethos eyepiece with 100-degree field of view

The Ethos 21mm is the model with the largest true field of view in the series. The 36.2mm field stop brings the field of view close to that of a 35mm Panoptic, while the exit pupil remains much smaller.

In an f/4 Dobsonian, that exit pupil is approximately 5.25 mm instead of 8.75 mm with a 35mm Panoptic. For older eyes and for observers under a light-polluted sky, that's a significant difference.

What a 100-degree field of view does

A classic Ploessl has 50 degrees, a Nagler has 82 degrees. At 100 degrees, your eye can no longer take in the field at once: you’re looking around the image instead of *at* it. That’s the effect the Ethos series is known for.

Practically, this also means that objects remain in view for longer. On a manually tracked Dobson, this saves constant readjustment.

The maximum field of view within a 2-inch pitch

At this focal length, the design is reaching the mechanical limit of the 2-inch holder. TeleVue is achieving the largest possible true field of view without significant edge vignetting.

The eyepiece is parfocal with the 31mm Nagler Type 5. Keep in mind that at over a kilo, it's the heaviest model in the series: check the balance of your mount.

Viewing Comfort and Dioptrx

The eye relief is 15 mm at every focal length in the series. The height of the foldable eyecup is adjustable, so your eye is always in the same position.

If you wear glasses due to astigmatism, you can replace them with Dioptrx on the eyepiece. This corrects your own cylindrical aberration without the eyeglass lenses costing contrast and eye distance.

In your telescope

In a telescope with a focal length of 1200 mm, this eyepiece provides approximately 57x with a true field of view of about 1.73 degrees. You can calculate this for your own telescope using the field stop: true field of view = 57.3 x field stop divided by the telescope's focal length.

The field stop on this model is 36.2 mm. That number—and not just the focal length—determines how much of the sky you actually see.

Included

• Foldable rubber eyecup
• Eyecup protector
• Dust cover for the stitch
• Filter thread abandoned

Featured accessories

Every Ethos eyepiece is compatible with the TeleVue Dioptrx, a corrector for astigmatism that allows you to observe without glasses. If you’re using a fast Newtonian, the Paracorr coma corrector will bring out that last bit of edge sharpness. For a 2-inch focuser, an Everbrite zenith mirror is the logical addition, and an eyepiece case protects your investment while on the go.

For whom yes and for whom no

• ✓ Vast Nebulae and the Milky Way
• ✓ Observers who want the widest field of view
• ✓ Fast Dobsonians where a small exit pupil is important
• ✗ Mounts that can't handle the weight
• Focusers without a 2-inch adapter

Specifications

All wide-angle eyepieces are on the page featuring wide-field eyepieces. You can find the complete selection of this merk on the TeleVue merk Page.