SVBONY SV188P Dielectric Mirror Star Diagonal - 99% Reflectivity

In this review the SVBONY SV188P Dielectric Mirror Star Diagonal is examined for backyard astronomers and casual observers who want a brighter, more comfortable eyepiece position. The bottom line: this 90 degree diagonal uses a super flat dielectric mirror that delivers over 99% reflectivity and a low-profile design that keeps the optical train well aligned. It is best for 1.25 in eyepiece users who value image clarity and secure eyepiece retention during adjustments.

Key Features

• Dielectric coatings: Provide an over 99% reflective surface that preserves light for brighter views of planets and the Moon.
• Super flat mirror: Keeps the optical path aligned so stars remain sharp across the field rather than appearing distorted.
• 90 degree viewing angle: Reflects the telescope's light path for comfortable observing of objects near zenith without neck strain.
• 1.25 in compatibility: Fits standard 1.25 in telescopes and accepts filters, eyepieces and Barlow lenses with a 1.25 in insert barrel.
• Brass compression ring: Built-in brass ring and thumbscrew secure eyepieces firmly while avoiding scratches to the barrel.

Who It's For

The SV188P is aimed at amateur astronomers using 1.25 in eyepieces who want improved light throughput and a comfortable 90 degree viewing position for long observing sessions. It suits those who appreciate a compact, well-built diagonal that aligns optically and accepts common accessories like filters and Barlow lenses.

Observers who need an erect image for terrestrial use or who require a mirror that preserves true left-right orientation should note this diagonal produces an upright image but will be left-right reversed in a 90 degree configuration. Also, users with 2 in systems will need a different diagonal size.

Pros & Cons

Pros

• High reflectivity dielectric coatings deliver a bright, clear view with minimal light loss.
• Solid build and low-profile 90 degree form that customers praised for alignment and appearance.
• Brass compression ring and thumbscrew keep eyepieces secure without scratching.

Cons

• Some users report mixed color accuracy, with occasional false color on certain targets or eyepieces.

Specifications

Brand	SVBONY
Model	SV188P
Connection size	1.25 in nosepiece
Reflective coating	Dielectric coatings, >99% reflectivity
Viewing angle	90 degree mirror diagonal
Retention	Brass compression ring with thumbscrew

Our Verdict

The SVBONY SV188P is a practical, well-made dielectric diagonal that offers genuine improvement in light throughput and comfortable viewing for 1.25 in eyepiece users. It is good value for observers who prioritize image clarity and solid mechanical retention, though those sensitive to subtle color shifts should be aware of mixed reports on color accuracy.

Frequently Asked Questions

Will this diagonal fit my 1.25 in eyepieces?
Yes, the diagonal accepts standard 1.25 in insert barrels and will work with eyepieces, filters and Barlow lenses sized to 1.25 in.

Does the diagonal correct image orientation?
The SV188P provides an upright view but will be left-right reversed when used at 90 degrees; it is not a mirror that gives a true non-reversed terrestrial orientation.

Is the mirror durable and secure?
The super flat dielectric mirror and the built-in brass compression ring with thumbscrew provide secure, scratch-free retention and stable alignment during use.