Orion 9 mm Sirius Plossl 1.25" Eyepiece
The Plossl 4-element design is renowned for its outstanding performance. Offering a wide 52° apparent field of view, Orion Sirius Plossl telescope eyepieces provide clear, sharp images of impressively high contrast. They're ideal for all types of telescopes: reflector, refractor, and catadioptric such as Maksutov-Cassegrains and Schmidt-Cassegrains. The 9 mm focal length is ideal for both deep sky objects as well as planetary viewing.
The Sirius Plossl optical system is fully coated with magnesium fluoride on every air-to-glass surface. Lens edges are blackened to both reduce scattering of stray light and maximize contrast.
The lens edges are mounted in black-anodized aluminum housings with 1.25" diameter barrels for durability and precision fit in 1.25" telescope focusers, or 2" focusers equipped with a step-down 1.25" eyepiece adapter (not included). Each barrel is internally threaded to accept 1.25" Orion filters. The built-in rubber eyeguards enhance viewing by helping to block out ambient light and properly position the eye.
- Apparent Field of View: 52°
- Number of Lens Elements: 4
Orion 9 mm Sirius Plossl 1.25" Eyepiece
The Orion Sirius Plossl eyepieces offer exceptional view at an affordable cost.
Orion Sirius eyepieces are designed to provide sharp, comfortable views. They are well suited for observing a wide range of celestial objects, including the Moon, planets, star clusters, nebulae, and galaxies. Each Sirius eyepiece features fully multi-coated optics to improve light transmission and reduce internal reflections. The design provides a well corrected field of view, allowing stars and other objects to remain sharp across much of the field. The eyepiece utilizes a “Fold-Up” eyecup, which allows an adjustable eye cup height for comfortable viewing. Orion Sirius eyepieces are threaded to accept standard 1.25 inch telescope filters.
- Features a premium 4-element lens design for exceptional clarity
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- Each lens is fully coated with anti-reflective finishes for maximum light transmission and high contrast detail
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- CNC-machined all-metal body delivering the utmost optical precision and durability
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- Complete with threading to accept standard 1.25” filters
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Explore the Cosmos with this Exceptional Eyepiece!
This quality crafted eyepiece provides wide and immersive window into the cosmos. Learn more about this premium eyepiece below!
9 mm Focal Length
To maximize the light gathering power of your telescope, it’s important to seek out an eyepiece with a focal length that compliments your telescope’s focal length. The ratio of telescope focal length and eyepiece focal length yields your system’s magnification, a key determinant not only in which celestial objects are available for viewing but also how clear your overall image will be based on your local seeing conditions. The formula for magnification is as follows: Telescope Focal Length ÷ Eyepiece Focal Length. The addition of this 9 mm focal length Sirius Plossl eyepiece with a standard 1200 mm focal length Dobsonian yields a magnification of 133x, making it optimal for up-close sights on bright, compact celestial objects. To take a deeper dive within this topic, take a look at our Ultimate Telescope Eyepiece Guide found within our Astronomy Hub.
Crafted with Quality in Mind
Each Orion Sirius Plossl eyepiece is crafted with the utmost care, ensuring exceptional performance for years to come. The CNC-machined all-metal body delivers a sleek, premium feel while simultaneously safeguarding the seven internal lenses and upholding precise optical alignment. While observing the cosmos, the soft rubber eyecups provide the utmost comfort.
Frequently Asked Questions
How do I calculate magnification?
Magnification can be calculated by taking your telescope’s focal length and dividing it by your eyepiece’s focal length. For instance, if we have an 8” 1,200 mm focal length Dobsonian telescope, and we’re using the 9 mm Emerald eyepiece, the magnification will be as follows: 1200/9 = ~133.3x. It’s important to note that magnification influences how bright your image will be, as the higher magnification, the dimmer your image will become (when using the same aperture). Be sure to check out our Ultimate Telescope Eyepiece Guide for more on this topic!
What’s the difference between apparent field of view (AFOV) and true field of view (TFOV)?
Apparent field of view refers to how large the image is to your eye. For reference, a single bare human eye has a field of view of approximately 150°. The Orion Sirius Plossl eyepieces offer an 52° AFOV for a well-immersed experience. True field of view, on the other hand, refers to the angular diameter of the “chunk” of the sky you are observing. TFOV is determined by dividing your AFOV by your system’s magnification. For instance, an 8” 1,200 mm focal length Dobsonian paired with the 9 mm Emerald eyepiece will yield a TFOV of 0.62°. The full disk of the Moon, for example, has an angular diameter of 0.5°. For more on this topic, our comprehensive Ultimate Telescope Guide provides an in-depth look!
What is exit pupil and why does it matter?
Exit pupil is the diameter of the beam of light that departs your eyepiece. It’s directly tied to the overall brightness of your image, and it’s an important factor to consider when determining which objects are available for observation. This term is analogous to our very own pupils, hence its name. As the pupil within our eye expands, more light is brought into our retina. This same concept is applicable to eyepiece exit pupils, with the larger the exit pupil, the brighter the image. Exit pupil and magnification go hand in hand; as magnification increases, exit pupil decreases, and vice versa. We measure the exit pupil by its diameter in millimeters. To calculate the exit pupil of your eyepiece/telescope combination, use either of the two equations: Exit Pupil = Telescope Aperture (mm) ÷ Magnification or Exit Pupil = Eyepiece Focal Length ÷ Telescope Focal Ratio.
Astronomy Hub: Your one-stop-shop for Astronomy Knowledge!
Our Gear Experts have compiled a wealth of information to help you get the most out of your telescope! Below you’ll find links to articles, videos and "how-to" guides. Just one more reason that our Astronomy Hub is a one-stop-shop for all your astronomy and astrophotography needs!
