Skywatcher 90° Star Diagonal Mirror 1.25 inch Eyepiece Adapter

For visual astronomers who demand a comfortable viewing posture without sacrificing image fidelity, the Skywatcher 90° Star Diagonal Mirror 1.25" offers a straightforward upgrade over straight-through viewing. Its 90-degree light path lets you observe near the zenith while keeping your neck relaxed, and the enhanced aluminum flat mirror maintains bright, high-contrast views across refractors, Schmidt-Cassegrains, and Maksutovs.

Highlights

• 90-degree star diagonal for ergonomic observing at high altitudes
• 1.25" barrel on both telescope and eyepiece sides for universal compatibility
• Enhanced aluminum mirror coating with >90% reflectivity
• Internal baffling reduces stray light and improves contrast
• Built-in 1.25" filter threads on the eyepiece barrel
• Durable aluminum alloy and ABS plastic housing with single set screw

In daily use

Slide the diagonal into any standard 1.25" focuser, secure it with the set screw, and insert your favourite eyepiece. The flat mirror delivers a correctly oriented image for terrestrial viewing and a mirror-reversed but upright image for astronomy—exactly what you expect from a star diagonal. The threaded eyepiece barrel accepts 1.25" filters directly, so you can add a moon filter or nebula filter without extra adapters. The compact body adds only a few centimetres to your optical train, preserving focus travel on most telescopes.

Full specifications

• Optical design: 90-degree star diagonal
• Eyepiece barrel size: 1.25" (31.7 mm)
• Telescope side barrel size: 1.25" (31.7 mm)
• Mirror type: Flat mirror
• Mirror coating: Enhanced aluminum
• Reflectivity: >90%
• Clear aperture: Approximately 27 mm
• Housing material: Aluminum alloy / ABS plastic
• Eyepiece holder: Single set screw
• Filter threads: Yes, 1.25" filter threads on eyepiece barrel
• Internal baffling: Yes
• Compatibility: Compatible with 1.25" focusers and eyepieces
• Application: Astronomical and terrestrial viewing
• Recommended telescope type: Refractors, catadioptrics (SCTs, Maks)
• Colour: Black

Final note

With its robust construction, high reflectivity, and thoughtful design, this star diagonal is an essential accessory for any 1.25" telescope setup, ensuring comfortable and detailed observations session after session.