Tele Vue Delos 4.5mm 72° Eyepiece - 1.25"

A Balanced Design: The 72° Field and 20mm Eye Relief

Each Delos model in Tele Vue's instruction sheet has 20mm of eye relief along with a 72° apparent field. At high power, a wider apparent field keeps a drifting planet in view longer in a telescope without a drive.

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. Eyeglass wearers should look for 15mm to 20mm of eye relief. The generous eye relief also minimizes eye lens fogging from eye moisture in cold weather.

High-Power Performance: Exit Pupils from 1.0mm to 0.3mm

The 4.5mm focal length is squarely in the high-power category, designed to reveal fine detail on the Moon, planets, and tight double stars. The exit pupil, the beam of light leaving the eyepiece, shrinks as the telescope's focal ratio rises. Tele Vue's chart gives 1.0, 0.9, 0.6, 0.5 and 0.3mm at f/4.5, f/5.2, f/7, f/10 and f/14. In an f/4.5 Newtonian the 1.0mm pupil suits globular clusters and small planetary nebulae.

In slower telescopes:

• At f/7 (Apo Refractors): A 0.6mm exit pupil, for the Moon and planets.
• At f/10 (SCTs/Maksutovs): A 0.5mm exit pupil, a very high power for the Moon and planets on steady nights.
• At f/14 (Long-Focus Maksutovs): A 0.3mm exit pupil, which needs excellent seeing.

Engineered for Comfort: 20mm Relief and the Locking Eyeguard

An eye too far in or too far out causes edge darkening and field loss, so with 20mm of eye relief it pays to learn your own position. The Delos 4.5mm has an adjustable, locking eyeguard housing in two pieces: twisting the lower grip ring to the left loosens it so it slides.

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. This also minimizes extraneous outside light, for the highest contrast on faint objects.

Paracorr, Dioptrx and Other Accessories

The Delos achieves sharpness, linearity and ghost suppression over the entire field for any speed (f/#) telescope. A fast Newtonian's own coma, comet-like stars toward the edge, is removed by the Tele Vue Paracorr Type-2; scopes faster than f/5.0 see the greatest results.

The Delos is ideal for the Tele Vue Dioptrx astigmatism corrector.

• Dioptrx Compatibility: A Dioptrx unit attaches and locks onto the top of the eyepiece and replaces your eyeglasses. It is always completely aligned to the eyepiece optics, unlike glasses.
• Accessory Ready: The FoneMate smartphone adapter clamps to compatible Tele Vue eyepieces for still, video or timelapse images, and the 1¼" barrel takes 1¼" filters (M28.5 x 0.6) such as Tele Vue's BandMate nebula filters.

Delos 4.5mm vs. Nagler & Ethos: Choosing Your High-Power View

Comparisons from Tele Vue's chart:

• vs. Ethos SX 4.7mm: The Ethos-SX has a 110° apparent field and an 8.9mm field stop, with 15mm of eye relief. The Delos 4.5mm has 20mm of eye relief and a 5.6mm field stop.
• vs. Nagler Type 6 5mm: The Nagler has an 82° field, a 7.0mm field stop and 12mm of eye relief, and needs an adapter for Dioptrx (Y*). The Delos 4.5mm is Dioptrx ready (Y).

The Delos 4.5mm gives up some field for 20mm of eye relief at high power.