SVBONY SV188 1.25″ 90° Mirror Diagonal for Refractors

Product Overview

The SVBONY SV188 is a 1.25″ 90° mirror star diagonal for refractors. It turns the light path through a right angle so the eyepiece sits at a comfortable position when you observe high in the sky. The mirror has a published reflectivity of 90%, the housing is metal, and a single thumbscrew holds 1.25″ eyepieces. The nosepiece fits 1.25″ focusers directly and 2″ focusers with an adapter.

Who It's For

This is a good match if you observe visually with a refractor that takes 1.25″ eyepieces and want an upright-angle viewing position for the Moon, planets and deep-sky objects, or if you need a replacement for a lost or damaged diagonal.

Key Features & Design

• 90° mirror diagonal: places the eyepiece at a right angle to the tube for comfortable viewing near the zenith.
• 90% reflectivity: the published reflectance of the mirror coating.
• Precision-machined alignment: SVBONY machines the mirror seat to hold optical alignment.
• Blackened internal threads: threaded baffling inside the barrel reduces glare and stray reflections.
• Metal housing with a single-screw 1.25″ eyepiece clamp.

Recommended Uses

• Lunar and planetary observing with a 1.25″ eyepiece set on a refractor.
• Deep-sky viewing near the zenith, where a straight-through view is awkward.
• Replacement diagonal for entry-level and travel refractors.

Compatibility and Accessory Notes

• Eyepiece side: 1.25″, one clamping screw.
• Telescope side: 1.25″ nosepiece; 2″ focusers need a 2″-to-1.25″ adapter.
• Telescope type: designed for refractors. SVBONY names refractors such as Celestron EQ and Meade Infinity models as examples.
• Not for Newtonians: a Newtonian's focal plane sits too close to the focuser for a diagonal to reach focus.

Good to Know Before You Order

• Mirror-reversed image: like all 90° mirror diagonals, it shows an upright image that is reversed left to right. For a fully correct image, an erecting prism diagonal is the alternative.
• Refractors (and similar) only: it is not suitable for Newtonian reflectors.
• Weight: SVBONY does not publish a weight for this diagonal.

Frequently Asked Questions

Is it difficult to set up?

No. It slides into the 1.25″ focuser and the eyepiece slides into the diagonal, each held by a thumbscrew.

Will it work in my 2″ focuser?

Yes, with a 2″-to-1.25″ adapter in the focuser.

Can I use it on a Newtonian?

No. SVBONY lists it as not suitable for Newtonians.

What is the image orientation?

Upright but mirror-reversed left to right, as with any single-mirror diagonal.

Bottom Line

In short: a 1.25″ 90° metal-bodied mirror diagonal with 90% reflectivity and blackened internal threads, for comfortable visual observing with a refractor.