The Delos High-Correction Optical Engine
At the heart of the Delos is a highly corrected optical system designed to render a flat, sharp field of view. By controlling for aberrations like astigmatism and chromatic aberration from the center to the very edge, the eyepiece delivers pinpoint stars across its entire expanse. This level of correction means you are not limited to the center of the field for critical observation; the view remains pristine as your eye drifts across it.
This optical precision translates directly into higher contrast on difficult targets. When viewing globular clusters, the sharp star points resolve more cleanly against the black background, allowing you to pick out individual members deeper into the core. On the Moon and planets, the absence of false color ensures that subtle details and natural color tones are preserved.
An Immersive 72° Apparent Field
The 72° apparent field of view provides a significant window on the sky that feels both expansive and comfortable. This field is wide enough to frame larger deep-sky objects, like the full expanse of the Andromeda Galaxy's core or the Beehive Cluster, without requiring you to pan your telescope. The experience is immersive, giving you a sense of looking through a porthole into space rather than a narrow tube.
The key trade-off in the Delos design is prioritizing perfect optical correction over achieving the absolute widest field possible. While eyepieces like the Nagler or Ethos offer larger fields, the Delos commits its entire 72° field to near-perfect fidelity. This makes it the right choice when image purity is more important than sheer field size.
Constant 20mm Eye Relief for Viewing Comfort
Every eyepiece in the Delos line features a constant, generous 20mm of eye relief. This is a deliberate design choice that ensures maximum comfort during long observing sessions, completely eliminating eye strain. For observers who wear glasses to correct for astigmatism, this long eye relief allows you to see the entire 72° field of view without removing your spectacles.
The fixed eye relief across the series also provides a consistent feel as you switch between different Delos focal lengths. Your head position and viewing posture remain the same, allowing you to concentrate on the object in view rather than readjusting your approach every time you change magnification.
Repeatable Eye Placement with a Locking Eyeguard
To make perfect use of the optical system, your eye must be positioned correctly. The Delos features an intuitive sliding eyeguard with a locking mechanism that allows you to set the ideal height and secure it in place. This mechanism ensures your eye returns to the exact same position every time you look into the eyepiece, preventing blackouts and kidney-beaning effects.
This practical feature is invaluable in the field. Once you find the sweet spot for your eye, you can lock it down, block out stray light from your surroundings, and maintain a comfortable, stable view throughout the night. It transforms the eyepiece from just a set of optics into a predictable and reliable observing tool.
Maximum Contrast through Advanced Coatings
To ensure the image is as bright and contrasty as possible, every air-to-glass surface in the Delos 17.3mm receives Tele Vue's proprietary index-matched multi-coatings. These advanced coatings maximize light throughput, resulting in brighter images of faint nebulae and galaxies. Furthermore, the edges of all lenses are blackened to absorb stray light that could otherwise reduce contrast and wash out fine detail.
The visual result is a deep, dark background sky that makes celestial objects "pop" in the field of view. When observing an object like the Orion Nebula through the Delos 17.3mm in a moderate aperture telescope, the faint outer loops of nebulosity are more easily visible, and the tightly packed stars of the Trapezium resolve cleanly without distracting glare.
Seamless Workflow with a Parfocal Design
The Delos 17.3mm is designed to be parfocal with all other Tele Vue Delos, Panoptic, Nagler, and Plössl eyepieces. This means that when you switch between any of these eyepieces, the need to refocus is dramatically reduced or eliminated entirely. This is a powerful workflow advantage that saves valuable time at the telescope.
Imagine locating an object with a low-power Panoptic and then swapping to the Delos 17.3mm for a closer look. With a parfocal system, the object snaps right into view with little to no adjustment of the focuser. This keeps your target centered and allows you to spend more time observing and less time hunting for focus in the dark.
How does the Delos 17.3mm compare to a Tele Vue Nagler eyepiece?
The Delos 17.3mm has a 72° apparent field of view and 20mm of eye relief, prioritizing optical purity and viewing comfort. A Nagler has a wider 82° field but shorter eye relief. Observers with eyeglasses or those who value a more relaxed view often prefer the Delos, while those seeking the most immersive "spacewalk" experience may choose the Nagler.
Is the 20mm of eye relief good for observers who wear glasses?
Yes, the 20mm of eye relief is excellent for eyeglass wearers. It allows you to keep your glasses on and still see the entire 72° field of view, which is critical if you need them to correct for astigmatism.
Will this eyepiece work well in my fast f/4.5 Dobsonian?
Yes, the Delos line is exceptionally well-corrected and performs superbly in fast telescopes. You can expect sharp stars across the entire field of view, even at f/4. For best results, pairing it with a Tele Vue Paracorr Type 2 will correct for the telescope's native coma.
What kind of targets is the Delos 17.3mm best for?
The 17.3mm focal length provides a versatile medium magnification. It is ideal for framing medium-to-large open clusters like the Pleiades, viewing globular clusters with high contrast, and observing large galaxies and nebulae like the Andromeda Galaxy or the Lagoon Nebula.
What is the purpose of the locking eyeguard?
The locking eyeguard allows you to set the perfect distance between your eye and the eyepiece lens for optimal viewing. Once you find this position, you can lock it, which prevents blackouts and ensures you get the full, comfortable field of view every time you look through it.
Is the Delos 17.3mm compatible with DIOPTRX?
Yes, the Delos 17.3mm is fully compatible with the Tele Vue DIOPTRX astigmatism corrector. This allows users with astigmatism to observe without wearing their glasses, while still achieving a perfectly sharp image.
