Tele Vue Delos 10mm 72° Eyepiece - 1.25"

The Delos 10mm: A 72° Field with 20mm of Eye Relief

Each Delos model has 20mm of eye relief along with a 72° apparent field. Al Nagler's guide puts Plössls at 50°, so the Delos shows a wider view at the same magnification.

Tele Vue's Ethos design experience made it possible to keep Delos size and weight down while achieving sharpness, linearity (freedom from pincushion distortion) and ghost suppression over the entire field for any speed (f/#) telescope.

Calculating True Field from the 12.7mm Field Stop

While apparent field describes the immersive quality of the view, the true field of view (TFoV) determines how much sky the eyepiece actually shows. This is governed by the eyepiece's field stop, a physical diaphragm inside the barrel, which for the Delos 10mm is 12.7mm in diameter.

You can calculate the true field for your specific telescope using Tele Vue's formula:

TFoV = (Eyepiece Field Stop ÷ Telescope Focal Length) x 57.3

• On a Tele Vue TV-85 (600mm FL): (12.7mm ÷ 600mm) x 57.3 = 1.21° true field.
• On a 10" f/10 SCT (2540mm FL): (12.7mm ÷ 2540mm) x 57.3 = 0.29° true field, room for Jupiter and its moons.

Exit Pupil and Magnification: Performance from f/4.5 to f/14

The exit pupil, the beam of light leaving the eyepiece, sets image brightness and how much detail your eye can use.

The exit pupil is calculated by dividing the eyepiece focal length by the telescope's focal ratio (f/#). Tele Vue's chart gives 2.2, 1.9, 1.4, 1.0 and 0.7mm at f/4.5, f/5.2, f/7, f/10 and f/14:

• f/4.5 Dobsonian: A 2.2mm exit pupil, for galaxies and bright nebulae.
• f/7 Apochromatic Refractor: A 1.4mm exit pupil, for globular clusters and planetary nebulae.
• f/10 SCT or Maksutov: A 1.0mm exit pupil, for the Moon and planets.
• f/14 Classical Cassegrain: A 0.7mm exit pupil, a high power for close double stars.

Ergonomics and Eyeglasses: 20mm of Relief with a Locking Eyeguard

The Delos is designed for optimum viewing whether or not you wear eyeglasses; with the eyeguard housing down, eyeglass wearers get the full eye relief. The generous 20mm of eye relief also minimizes eye lens fogging from eye moisture in cold weather. To set your eye position, the Delos has an adjustable, locking eyeguard.

Twist the lower grip ring to the left to loosen the housing, slide it to full extension, then slide it down while looking through the eyepiece until you just see the full field with your peripheral vision. Green indicator lines on the inner barrel record your height, and twisting the lower grip ring to the right locks it. This also minimizes extraneous outside light, for the highest contrast on faint objects.

Sharpness and Linearity at Any f-Ratio

The Delos keeps its sharpness over the entire field for any speed (f/#) telescope, which matters most in fast telescopes such as Dobsonians. A fast Newtonian's own coma still needs a corrector (see below).

Linearity means freedom from pincushion distortion: straight lines stay straight and objects keep their shape as they drift toward the edge.

Using the Delos 10mm with a Paracorr or Powermate

Two Tele Vue accessories change how the Delos 10mm works in a given telescope.

• Paracorr Type-2: Fast Newtonians show coma, which no eyepiece removes. The Paracorr Type-2 eliminates it, with the greatest results in scopes faster than f/5.0. Its 1.15x magnification factor makes the Delos 10mm act like an 8.7mm.
• Barlows and Powermates: You can increase the magnification of the Delos 10mm using Tele Vue's image amplifiers. A 2x Powermate converts it to a 5mm eyepiece, while a 2.5x Powermate yields a 4mm equivalent, for high-power planetary views.

Delos 10mm vs. Ethos 10mm and Nagler 9mm: Choosing Your View

Within the Tele Vue lineup, the Delos 10mm occupies a specific niche defined by its balance of field width, eye relief, and optical purity. Its primary counterparts are the 10mm Ethos and the 9mm Nagler Type 6.

• vs. Ethos 10mm: The Ethos has a 100° apparent field and a 17.7mm field stop, so it shows more sky, with 15mm of eye relief. The Delos 10mm has 20mm of eye relief and a 12.7mm field stop.
• vs. Nagler 9mm Type 6: The 9mm Nagler has a wider 82° apparent field with 12mm of eye relief and needs an adapter for Dioptrx (Y*). The Delos 10mm has 20mm of eye relief and is Dioptrx ready (Y). Eyeglass wearers are best served by 15mm to 20mm of eye relief.

Dioptrx, FoneMate and Filters

The Delos manual lists these Tele Vue accessories:

• DIOPTRX™ Ready: The Delos is ideal for Tele Vue's Dioptrx astigmatism corrector, which locks onto the top of the eyepiece, stays aligned to the eyepiece optics and replaces your glasses at the eyepiece.
• FoneMate™ Compatible: The FoneMate smartphone adapter clamps to compatible Tele Vue eyepieces for still, video or timelapse images.
• Bandmate™ Filter Ready: The 1¼" barrel takes 1¼" filters (M28.5 x 0.6). BandMate Nebustar, O-III and H-Beta filters make nebulae "pop out" by passing select wavelengths and darkening the sky.