Eyepiece Tele Vue Delos 17.3mm 1.25-inch EDL-17/3 72° apparent field

The Tele Vue Delos 17.3mm 1.25-inch eyepiece EDL-17/3 provides a 72° apparent field designed for visual astronomy. With a medium focal length, this eyepiece balances magnification and field of view to offer comfortable observing of planets, the Moon, star clusters and many deep-sky objects. The Delos design emphasizes extended eye relief and a flat, well-corrected field to reduce edge aberrations and support relaxed viewing during longer sessions.

Advantages

The eyepiece combines a wide 72° apparent field with generous eye relief, making it easier to frame objects and track them without frequent repositioning. Optics are engineered for sharpness across much of the field, reducing coma and field curvature common in simpler eyepieces. The 1.25-inch barrel fits standard visual backings and accessory chains, and the mechanical design includes features intended to maintain comfortable eye position and repeatable centering.

Suitable for

• Visual planetary and lunar observation at moderate to high power
• Wide-field views of open star clusters and larger deep-sky objects
• Observers who need comfortable eye relief for extended sessions
• Telescopes with 1.25-inch focuser fittings and visual use setups

When it may not be suitable

This eyepiece is a medium-focal-length visual eyepiece rather than a dedicated planetary high-power or ultra-wide-field eyepiece. It may not be the best choice for extreme high-magnification planetary imaging or for users seeking the widest possible apparent field beyond 72°. For photographic or CCD imaging, a design specifically intended for imaging may be preferable.

Key specifications

• Focal length: 17.3 mm
• Apparent field of view: 72°
• Barrel diameter: 1.25 inch
• Designed for visual observing with extended eye relief

How to use

Insert the 1.25-inch barrel securely into your telescope focuser or diagonal and tighten the retaining thumbscrew to prevent rotation. Start focusing at low to moderate magnification and adjust fine focus until the target appears sharp across the field. Use the extended eye relief to position your eye comfortably; this facilitates observing with eyeglass wearers or during long sessions. For best results allow the telescope to reach thermal equilibrium and collimate the optics before high-power use.

What to consider before purchase

• Compatibility with your telescope focuser (1.25-inch barrel required)
• Whether a 17.3 mm focal length and 72° field fit your observing priorities
• Need for extended eye relief if you wear glasses or prefer relaxed viewing
• Intended use: visual observing versus imaging

Usage recommendations

Use the Delos 17.3mm eyepiece for medium-power visual sessions—start with bright targets such as the Moon and planets to evaluate centering and sharpness, then move to star clusters and larger nebulae to appreciate the 72° field. Ensure the telescope is well-collimated and thermally stable to maximize edge-to-edge performance.