What Are 90° Amici Prisms and Why Use Them?
A 90° Amici prism is a specialized optical element designed to redirect a light beam by 90 degrees while correcting the orientation of the image. Unlike standard diagonal mirrors, this prism delivers a direct, non-inverted image that is ideal for observing both terrestrial objects and astronomical bodies. It is used primarily with refractors and catadioptric telescopes, where the standard eyepiece position is not ergonomically convenient. Thanks to precisely ground optical glass, it ensures minimal distortion and high light transmission. 90° Amici prisms for telescopes are a popular choice among astronomers and nature observers alike. Their versatility makes them a worthwhile addition to any optical setup.
Advantages of Amici Prisms Over Standard Diagonal Mirrors
Standard diagonal mirrors do redirect the view by 90°, but the image remains mirror-reversed, which can be disorienting during extended observation sessions. Amici prisms solve this problem elegantly through their unique geometry, which preserves the natural, upright orientation of the image. This is especially important when observing landscapes, birds, or distant terrestrial objects, where a reversed image interferes with spatial orientation. Astronomers will also appreciate the correct image orientation when star-mapping or tracking planetary movement. The higher image quality and natural view without inversion make Amici prisms a truly versatile accessory for any telescope. Their robust construction also ensures long-lasting, reliable performance in the field.
Key Features of 90° Amici Prisms
- Precise 90° redirection of the light path
- Non-inverted, direct image without mirror reversal
- High light transmission due to quality optical glass
- Compatibility with 1.25″ and 2″ eyepieces
- Sturdy and durable construction for long-term use
- Suitable for both terrestrial and astronomical observation
How to Choose the Right Amici Prism for Your Telescope?
When selecting an Amici prism, the most important parameter is the diameter of your telescope's focuser draw tube. The most common prisms fit the standard 1.25″ diameter, which is compatible with the vast majority of small and medium telescopes. For larger apertures and premium instruments, 2″ prisms are available, allowing more light to pass through and making better use of high-power eyepieces. The quality of the optical glass also matters - prisms made from BaK-4 or borosilicate glass with full multi-coatings deliver the best contrast and color fidelity. Before purchasing, check whether the prism includes a filter thread and whether its length will still allow focus to be achieved with your instrument. Consulting our product specialists can also help you find the perfect match for your setup.
Main Parameters of Amici Prisms at a Glance
- Beam deflection angle: 90°
- Eyepiece barrel diameter: 1.25″ or 2″
- Glass type: BaK-4 or borosilicate
- Light transmission: 95-99%
- Image orientation: direct, non-inverted
Amici Prisms for Terrestrial and Astronomical Use
One of the greatest strengths of the Amici prism is its dual-purpose nature - it performs equally well for daytime nature watching and nighttime stargazing. When used during the day, observers benefit from a correctly oriented image that makes it easy to follow moving subjects such as birds or wildlife. At night, the prism simplifies star-chart navigation by presenting the sky in its natural orientation rather than a mirror-reversed view. The minimal light loss through quality coated glass ensures that faint objects remain visible even under challenging conditions. This makes the Amici prism a smart investment for anyone who wants a single accessory that works across a wide range of observing scenarios.
Browse Our Catalogue of 90° Amici Prisms
Buy a 90° Amici prism today from the comfort of your home in our online astronomy and optics store. We offer models from trusted manufacturers such as Baader Planetarium, Celestron, Vixen, and Sky-Watcher, all of which have passed strict quality checks. Each prism comes in a protective case along with the necessary adapters for easy installation. Our knowledgeable advisors are happy to help you select the prism that best suits your telescope and observing style. All items available in stock are typically dispatched within two business days.
