Omegon Pro 45° pentagonal prism 1.25″
The Omegon Pro pentagonal prism is a five-sided optical element designed for refractors and catadioptric telescopes. Unlike a conventional diagonal mirror - which erects the image but also flips it horizontally - a penta prism delivers an inverted image that matches the view through a telescope used without any diagonal. This means the image orientation corresponds directly to standard star charts and moon maps, with no need for any mental rotation. Simply turn your map 180° and the orientation is immediately correct - a real advantage for anyone who works with atlases or plans to observe lunar craters.
Why choose a pentagonal prism over a standard diagonal?
When using a conventional mirror diagonal, you have to mentally mirror-flip the image to match it to a star chart - which is genuinely impractical at night when you are searching for a specific crater or a faint star. The Omegon Pro pentagonal prism solves this problem elegantly: the image orientation corresponds exactly to the view through a refractor without a diagonal, making map work intuitive and fast. This is especially valuable when mapping the Moon in detail or locating objects in dense star fields, as you never have to mentally translate what you see.
Optics and construction
The prism is manufactured from BK-7 glass and uses dielectric mirrors with a multi-layer anti-reflection coating. The result is a brilliant, high-contrast, and exceptionally bright image that surpasses even a quality Amici prism. The unique geometry of the penta prism eliminates a common problem found in other prisms - the disturbing influence of edges on image quality. Light entering the prism always changes direction by exactly a right angle (in the 45° version), regardless of the angle of incidence, which guarantees consistent optical performance under all conditions.
- BK-7 glass optical element
- Dielectric mirrors with multi-layer anti-reflection coating
- Blackened interior surfaces for maximum contrast
- Light-tight body - no stray light affecting image contrast
- 29 mm clear aperture - no vignetting even with wide-angle eyepieces
- 1.25″ fitting with spring-loaded safety retention system
- Standard 1.25″ filter thread
Compatible eyepieces and filters
The 29 mm clear aperture allows full use of long focal length eyepieces as well as wide-field eyepieces without any vignetting, so there is no need to restrict your eyepiece selection. The 1.25″ holder is equipped with a spring-loaded safety retention system and a standard 1.25″ filter thread for convenient filter use.
Who is this prism for?
The Omegon Pro pentagonal prism is the ideal choice for astronomers who regularly work with star atlases, moon maps, or planetary charts, and who want the telescope image orientation to match what they see on paper or on screen. It is equally well suited as a reliable, optically excellent prism for everyday visual observing where high contrast and image brightness matter.
| Parameter |
Value |
| Type |
Pentagonal (penta) prism |
| Angle |
45° |
| Barrel size |
1.25″ |
| Clear aperture |
29 mm |
| Glass type |
BK-7 |
| Coating |
Dielectric multi-layer anti-reflection |
| Filter thread |
Standard 1.25″ |
| Image orientation |
Inverted (no lateral flip) - matches star charts |
