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Diagonals


Diagonals
Star diagonals provide a more comfortable viewing angle when using refractors, Maksutov-Cassegrain, or Schmidt-Cassegrain telescopes. Upgrading the diagonal from 1.25-inch format is often beneficial as this will allow the use of 2-inch eyepieces. Owners of Schmidt-Cassegrain telescopes larger than eight inches in aperture should seriously consider upgrading to a 2-inch diagonal.

Diagonals

Celestron 1.25-inch Errect Image 45 Degree Diagonal
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$35.00
Celestron 1.25-inch Star Diagonal
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$35.00
Celestron 2-inch SCT Diagonal XLT
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$139.00
Meade Series 5000 2" Diagonal Mirror
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$149.99
Orion 1.25-inch 45-degree Correct Image Diagonal
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$69.00
Orion 1.25-inch Correct-Image Star Telescope Diagonal
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$69.99
Orion Dielectric Mirror Star Diagonal 1.25-inch
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$109.00
Orion Dielectric Mirror Star Diagonal 2-inch
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$155.00
Stellarvue 1.25-inch Erecting Prism
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$69.00
Stellarvue 2" Dielectric Star Diagonal
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$189.00
TeleVue 2-inch Everbrite Diagonal Package
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$320.00 $310.00

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TeleVue 2-inch Schmidt-Cassegrain Diagonal Package
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$371.00 $359.00

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TeleVue 45 Degree Erecting Prism 1.25"
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$59.00
TeleVue 60 Degree Everbrite 1.25"
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$239.00
TeleVue 90 Degree Enhanced Aluminim Diagonal 1.25"
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$130.00
TeleVue 90 Degree Everbrite Diagonal 1.25"
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$185.00
TeleVue Long SCT Adapter
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$48.00

Buy Telescope Star Diagonals

When you aim a refractor, SCT or Maksutov_Cassegrain telescope up at the night sky, the light cone exiting the telescope points downwards. This can make for an awkward viewing experience, as the higher the telescope points, the closer to the ground you have to be to see through it.

Star diagonals, also known as telescope diagonals, fix these problems, providing a more comfortable viewing angle. The only telescope type that doesn’t need a star diagonal is the Newtonian reflector, which has a focuser that points out sideways from the top of the telescope

Telescope star diagonals are simple accessories, deflecting the light from a telescope by 90 degrees. All the viewer needs to do is slide the telescope diagonal into the focuser. Star diagonals work in one of two ways:

  • Prism: Prism star diagonals use a triangular-shaped prism, with the base of the prism positioned at 45 degrees. When the incoming light hits the base of the prism, it’s deflected by 90 degrees, so it goes into the eyepiece. The light path in a prism diagonal is slightly longer than that of a mirror diagonal, and prisms tend to be more prone to chromatic aberration. However, prisms don’t degrade over time and transmit as much light as a mirror, producing high-contrast images for a longer period than most regular mirror diagonals.
  • Mirror: Mirror diagonals work similarly to prism star diagonals, with a mirror oriented at exactly 45 degrees to the incoming beam of light so the light is reflected directly into the eyepiece. The efficacy of these mirror diagonals depends on the high reflectance of the mirror, which is why dielectric diagonals, using dielectric mirrors, are so popular — they reflect up to 99% of incident light, producing a brighter image. Dielectric mirrors also don’t degrade over time, unlike regular mirrors.

Diagonals are available in multiple sizes, but upgrading the diagonal from 1.25-inch format to a 2-inch star diagonal is often beneficial as it would allow the use of 2-inch eyepieces. Owners of Schmidt-Cassegrain telescopes larger than eight inches in aperture should seriously consider upgrading to a 2-inch diagonaldielectric mirror diagonal.

Skies Unlimited offers quality star diagonals from a variety of brands, including Tele Vue and Stellarvue star diagonals. We also provide the expertise you need to make the best decision for your viewing needs.

Established in 2004 by amateur astronomers striving to make astronomy more accessible to the masses, Skies Unlimited strives to provide our customers with the equipment they need along with the knowledge and advice to support them in their new hobby. No matter what you need, from advice on recommendations to product specifications, we’re here to help.

Learn More Today

Lookinf for a new star diagonal? Skies Unlimited can help. Call us today or visit our store located just outside of Pottstown, Pa., and we’ll get you the information you need to continue improving your observational experience.