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Orion Telescopes
Orion 1.25" Pentaprism Diagonal
Accepted Payment
Expected Ship Date: 09/09/2024

  • The Orion Pentaprism Diagonal is ideal for use with the Orion Premium Linear BinoViewer, because the combination renders an upright, non-mirror-reversed image.
  • The Pentaprism Diagonal incorporates a pentagonal-shaped prism of BK-7 glass that is multi-coated and dielectric coated for maximum light transmission.
  • It features a 1.25" non-marring compression ring collar and a tapered barrel for secure attachment to a telescope.
  • With a generous clear aperture of 29mm, the Pentaprism Diagonal will not cause image vignetting, even when used with long focal length, wide-field eyepieces.

Learn more
Item #  52055

The Orion Pentaprism 90-Degree Diagonal is a non-inverting, non-reversing 1.25" diagonal with a 90-degree viewing angle. Unlike a star diagonal, it does not produce a mirror-reversed image, which can make navigation and referring to star maps while observing with your telescope difficult. But unlike a correct-image diagonal, there is no image degradation caused by the ridge line where prisms intersect, which especially affects high-power viewing. It is the only diagonal that can be used with the Orion Premium Linear BinoViewer to render an upright, non-mirror-reversed image through a telescope. So we highly recommend it for viewing with the Premium Linear BinoViewer, especially for terrestrial applications for which a correctly oriented view is a must.

As its name implies, the Pentaprism diagonal consists of a pentagonal-shaped prism, which is made of BK-7 glass that is multi-coated on its two transmitting surfaces and dielectric coated on its two reflective surfaces, for maximum light transmission to the eyepiece. The pentaprism is housed in a black-anodized aluminum body that features a non-marring 1.25" compression ring collar with a large knurled thumbscrew, and a tapered 1.25" barrel that is threaded for use of filters.

The Orion Pentaprism diagonal has an optical path length (backfocus requirement) of 120mm, and a generous clear aperture of 29mm. One nice feature of the Pentaprism diagonal is that it causes no vignetting, even when used with long focal length, wide-angle eyepieces. When used in combination with just an eyepiece, the Pentaprism diagonal will render an upside-down image, but not mirror reversed as you get with a standard star diagonal. That can be advantageous for telescopic viewing with star charts, since you need only rotate the star chart to match the view in the eyepiece. A mirror-reversed eyepiece view, on the other hand, requires some mental gymnastics when referring to a star map! While the Pentaprism is the ideal diagonal to use with the Orion Premium Linear BinoViewer, note that it may not provide a correctly oriented view with other binoviewers, which unlike the Premium Linear BinoViewer typically do not incorporate an image erecting lens system.

Try this premium quality Orion Pentaprism diagonal — especially if you plan to observe with the Orion Premium Linear BinoViewer. It's the "best and brightest" diagonal for the job!


Limited Warranty against defects in materials or workmanship for one year from date of purchase. This warranty is for the benefit of the original retail purchaser only. For complete warranty details contact us at 800-447-1001.


Please note this product was not designed or intended by the manufacturer for use by a child 12 years of age or younger.

  • User level
  • Barrel size
  • Coatings
  • Filter threads
  • Compression ring
  • 2"-1.25" adapter
    Sold separately
  • Weight (oz.)
  • Additional included accessories
  • Other features
  • Warranty
    One year

Pentaprism Diagonal
Dust Caps (x2)

Orders received by 1pm Eastern Standard Time for in-stock items ship the same business day. Order received after noon will ship the next business day. When an item is not in-stock we will ship it as soon as it becomes available. Typically in-stock items will ship first and backordered items will follow as soon as they are available. You have the option in check out to request that your order ship complete, if you'd prefer.

A per-item shipping charge (in addition to the standard shipping and handling charge) applies to this product due to its size and weight. This charge varies based on the shipping method.

Standard Delivery: $0.00
3 Day Delivery: $10.00
2 Day Delivery: $10.00
Next Day Delivery: $20.00

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