Tele Vue Delos 3.5mm 72° Eyepiece - 1.25"

A 72° Field and a 4.4mm Field Stop

Each Delos model has 20mm of eye relief along with a 72° apparent field. The Delos achieves sharpness, linearity (freedom from pincushion distortion) and ghost suppression over the entire field for any speed (f/#) telescope.

The true field of view you see is determined by this 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 a telescope with a 1000mm focal length, the Delos 3.5mm yields a true field of (4.4mm ÷ 1000mm) x 57.3 = 0.25°, enough for Jupiter with its inner moons when they lie close to the planet.

3.5mm Focal Length: Exit Pupils Down to 0.3mm

With its 3.5mm focal length, this eyepiece is built for the highest practical magnifications your telescope and the night sky will allow. Magnification is calculated by dividing your telescope's focal length by the eyepiece's; a 1200mm telescope will achieve 343x with the Delos 3.5mm. That much power is for close double stars and for planets on the steadiest nights.

The exit pupil, or the beam of light exiting the eyepiece, is a critical factor for high-power viewing. Small exit pupils darken the sky background. Tele Vue's chart gives:

• 0.8mm in an f/4.5 telescope
• 0.7mm in an f/5.2 telescope
• 0.5mm in an f/7 telescope
• 0.4mm in an f/10 telescope
• 0.3mm in an f/14 telescope

Consistent 20mm Eye Relief with an Adjustable 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 20mm of eye relief. The generous eye relief also minimizes eye lens fogging from eye moisture in cold weather.

The adjustable, locking eyeguard housing comes in two pieces. Twisting the lower grip ring to the left loosens it. Without glasses, slide it fully out, then 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. An eye too far in or out causes edge darkening and field loss.

Paracorr, Powermates and Other Accessories

Fast Newtonians show coma, comet-like stars toward the edge, which no eyepiece removes. The Tele Vue Paracorr Type-2 eliminates it; scopes faster than f/5.0 see the greatest results. It has a 1.15x magnification factor, so the Delos 3.5mm acts like a 3.0mm.

A 2x Powermate would make it act like a 1.75mm eyepiece, a power few telescopes or nights can use. The Delos manual also lists:

• DIOPTRX: The Delos is ideal for the Tele Vue DIOPTRX astigmatism corrector, which locks onto the top of the eyepiece and replaces glasses.
• Bandmate Filters: The 1¼" barrel takes 1¼" filters (M28.5 x 0.6).
• FoneMate: The FoneMate smartphone adapter clamps to compatible Tele Vue eyepieces for still, video or timelapse images.

Delos 3.5mm vs. Nagler & DeLite: Choosing Your High-Power Eyepiece

Comparisons from Tele Vue's chart:

• vs. Nagler Type 6 3.5mm: The Nagler has an 82° apparent field, a 4.8mm field stop and 12mm of eye relief, and needs an adapter for Dioptrx (Y*). The Delos has a 72° field, a 4.4mm field stop and 20mm of eye relief, and is Dioptrx ready (Y).
• vs. DeLite 3mm & 4mm: The DeLites also have 20mm of eye relief and are Dioptrx ready, with a 62° apparent field; the 4mm has a 4.3mm field stop and the 3mm a 3.2mm field stop. The Delos 3.5mm has the wider 72° field.