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Explore Scientific 99% Reflective Diagonal - 3"
The Explore Scientific 3-inch Dielectric Diagonal uses a first-surface mirror with a 99% reflective coating to deliver the brightest possible image from your telescope's focal plane to the eyepiece. Designed for telescopes with large 3-inch focusers, this diagonal includes a 2-inch adapter, ensuring it can securely hold the most common large-format eyepieces and imaging accessories.
99% Dielectric Coating: Maximizing Light Throughput to Your Eyepiece
A diagonal's primary job is to preserve the light collected by your telescope's main optic. The multi-layer dielectric coating on this mirror reflects 99% of incoming light, a noticeable improvement over standard aluminum or even enhanced aluminum coatings. This increase in brightness is especially critical when observing faint deep-sky objects like the Veil Nebula (NGC 6960) or distant galaxies where every photon counts.
Secure Mechanical Design: 3-Inch Body with Compression Rings and a Safety Taper
This diagonal is built for both stability and safety. Eyepieces are held in place by a brass compression ring on the included 2-inch adapter, which prevents the marring and scratching caused by simple set screws. The 3-inch insert barrel features a double taper, a crucial safety feature that prevents the diagonal from slipping out of the focuser if the locking screw becomes loose.
3-Inch vs. 2-Inch Diagonals: Why the Larger Format Matters
While a 2-inch diagonal is sufficient for most visual astronomy, a 3-inch model is essential for preventing vignetting in specific applications. Large refractor telescopes and astrographs with 3-inch or larger focusers can illuminate a very wide field, and a 3-inch diagonal ensures that the light cone is not cut off before it reaches a full-frame imaging sensor or an extreme wide-field 2-inch eyepiece.
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For Imagers: If you are using a large-format CMOS or CCD camera, a 3-inch diagonal provides a larger clear aperture to fully illuminate the sensor and avoid darkened corners in your images.
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For Visual Observers: While not always necessary, it provides peace of mind that your widest 2-inch eyepieces are operating without any restriction from the diagonal itself.
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What is the main benefit of the Explore Scientific 3-inch Diagonal's 99% reflectivity?
The 99% reflectivity from its dielectric coating ensures maximum light transmission from your telescope to your eyepiece. This results in brighter images, which is especially important for viewing faint deep-sky objects like nebulae and galaxies, compared to standard diagonals which may only reflect 90-96% of the light.
Will the Explore Scientific 3-inch Diagonal fit my telescope?
This diagonal is designed specifically for telescopes equipped with a 3-inch focuser. It will not fit standard 1.25-inch or 2-inch focusers. It is most commonly used with large apochromatic refractors and Ritchey-Chrétien telescopes designed for wide-field imaging.
Why would I need a 3-inch diagonal instead of a 2-inch for my large refractor?
For a large refractor with a 3-inch or larger focuser, a 3-inch diagonal is critical for preventing vignetting (darkening at the edges of the field of view). This is most apparent when using full-frame imaging sensors or very long focal length, wide-field 2-inch eyepieces that utilize the entire light cone produced by the telescope.
How does the Explore Scientific 3-inch diagonal prevent damaging my eyepieces?
The included 2-inch adapter uses a brass compression ring to secure eyepieces. When you tighten the lock screw, the ring gently and evenly tightens around the eyepiece barrel. This provides a more secure grip than a single set screw and prevents the screw from digging into and scratching the barrel of your expensive eyepieces.
I'm imaging the Andromeda Galaxy (M31) with a full-frame sensor; will this 3-inch diagonal help?
Yes. Imaging a large target like the Andromeda Galaxy (M31) with a full-frame sensor is exactly the scenario where a 3-inch diagonal is most beneficial. It ensures the entire sensor is evenly illuminated by your telescope's light cone, preventing the vignetting that a smaller 2-inch diagonal would likely cause at the corners of your image.
Does the Explore Scientific 3-inch diagonal include an adapter for 1.25" eyepieces?
No, this diagonal comes standard with a 2-inch adapter only. A separate 2-inch to 1.25-inch adapter would be required to use 1.25-inch eyepieces, though this is not a typical use case for a diagonal of this size.
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| GTIN |
812257014774 |
| Size |
3-inch |
| Reflectivity |
99% Dielectric |
| Included Adapter |
2-inch |
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This product's "What's in the Box" information is currently unavailable.
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This product's manuals and software are not available for download at this time.
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Explore Scientific Warranty
