Explore Scientific 99% Reflective 3" Diagonal

Explore Scientific 99% Reflective 3" DiagonalA 3 inch dielectric coated star diagonal that reflects 99% of incoming light through a full 3 inch optical path designed for telescopes with 3 inch focusers where a standard 2 inch diagonal would vignette the light cone and clip the edges of wide field views. The first surface dielectric coating reflects virtually all incoming light, delivering the brightest and highest contrast image your telescope can produce. This is particularly important at the 3

A 3-inch dielectric-coated star diagonal that reflects 99% of incoming light through a full 3-inch optical path — designed for telescopes with 3-inch focusers where a standard 2-inch diagonal would vignette the light cone and clip the edges of wide-field views.

The first-surface dielectric coating reflects virtually all incoming light, delivering the brightest and highest-contrast image your telescope can produce. This is particularly important at the 3-inch aperture class, where the telescopes paired with this diagonal are typically fast, large-aperture refractors — instruments where every fraction of a percent of light transmission matters for deep-sky performance.

The double-taper insert barrel slides smoothly into 3-inch focusers and the wider taper section prevents the diagonal from accidentally falling free. A compression ring lock secures eyepieces without set screw marks. Includes a 2-inch adapter so you can use your existing 2-inch eyepiece collection, and dust covers to keep optics clean in storage.

Key Features

• 99% first-surface dielectric coating for maximum brightness
• Full 3" optical path — eliminates vignetting on large-format focusers
• Double-taper insert barrel for secure, smooth fit
• Compression ring eyepiece lock — no set screw marks
• 2" adapter and dust covers included
• Weight: 2.0 lbs (0.90 kg)

Ideal For

• Large refractor owners — the ES ED152, FPL53-series, and other 3"-focuser telescopes need a 3" diagonal to avoid vignetting
• Deep-sky visual observers — the full 3" light path paired with 99% dielectric reflectivity delivers the brightest possible wide-field views
• 2" eyepiece users — included adapter means your existing eyepieces work immediately

Good to Know

• 1.25" eyepiece adapter is sold separately
• Designed for telescopes with a 3" focuser — will not fit standard 2" focuser drawtube