Orion 45 Erect-Image Prism Diagonal - 1.25"For terrestrial viewing with a refractor or Cassegrain telescope, use of a correct-image (or image erecting) prism diagonal may be desirable. The image through the eyepiece image will appear upright and non-reversed, matching the naked-eye orientation. So a correct-image diagonal is essential for terrestrial viewing with the above telescope types and is useful for astronomical viewing for those that prefer to have the view through the telescope match the naked-eye orientation.
Orion has three correct-image diagonals to choose from: a 45-deg 1.25" version, a 90-deg 1.25" version, and a 90-deg 2" model (with 1.25" collar). All are fully multi-coated and threaded for filters. Note that the 45-deg Orion Correct-Image Prism Diagonal requires 5/8" more focus travel than typical diagonals. Diagonals are not recommended for use in reflector telescopes.
- For terrestrial or astronomical use, this diagonal produces a right-side-up, non-reversed image with correct daytime orientation
- Fully coated prisms for superior image fidelity and maximum light throughput
- Accepts 1.25" eyepieces, fits in 1.25" focusers
- Not recommended for use in Newtonian reflector or Dobsonian reflector telescopes
- Requires 5/8" more focus travel than typical star diagonals
Questions & AnswersAsk a Question
What can I use for a reflector telescope please?
Most reflector telescopes will not reach focus with any added 45 degree diagonal, as the diagonal takes up ~3" (~76mm) of back focus. If your eyepiece focuses on your scope before you have moved the focuser at least 76mm outward from the lowest position,
Will putting this part require an extension on the telescope to achieve a correct focus?
No, It will work with a refactor telescope without any extra extensions.