Binorum Kellner 20mm 50° 1.25″ Eyepiece
Time-Tested Design for Budget-Conscious Astronomers
The Kellner eyepiece design has served amateur astronomers reliably for over a century, offering clear views of celestial objects at an accessible price point. The Binorum Kellner 20mm continues this tradition, providing a solid optical foundation for observers who want quality performance without premium pricing. With its classic 3-element construction and 50° apparent field of view, this eyepiece represents excellent value for beginners and experienced astronomers alike.
Versatile 20mm Focal Length for Wide-Field Views
The 20mm focal length makes this eyepiece particularly versatile for low to medium magnification observations. Whether you're scanning the lunar surface, viewing open star clusters, or exploring large nebulae, the Kellner 20mm provides a comfortable balance between magnification and field of view. The 50° apparent field creates an immersive observing experience while maintaining good eye relief for relaxed viewing sessions.
Suitable for Refractor and Reflector Telescopes
The eyepiece is suitable for basic refractor and reflector telescopes, making it an ideal choice for observers starting their astronomical journey or adding to their eyepiece collection. The universal 1.25″ barrel diameter ensures compatibility with virtually all modern amateur telescopes, while the straightforward optical design performs well across different telescope types and focal ratios.
Key Features
- Classic Kellner 3-element optical configuration for reliable image quality
- 50° apparent field of view for comfortable wide-field observations
- 1.25″ barrel diameter - universal compatibility with modern telescopes
- Multi-coated optics for improved light transmission
- Metal barrel construction for long-term durability
- Filter threads for adding moon filters or color filters
- Rubber eyecup for viewing comfort and stray light protection
- Excellent price-to-performance ratio for budget-conscious observers
Technical Specifications
- Focal length: 20mm
- Apparent field of view: 50°
- Barrel diameter: 1.25″ (31.7mm)
- Optical design: 3-element Kellner configuration
- Lens coatings: Multi-coated
- Eye relief: Approximately 15mm (comfortable for most observers)
- Filter threads: Standard 1.25″ threads
Ideal Magnification for Multiple Observing Programs
The 20mm focal length delivers practical magnifications across a range of telescope types. With a 600mm focal length telescope, this eyepiece provides 30x magnification - perfect for viewing the entire lunar disk or large star clusters like the Pleiades. Paired with a 1000mm telescope, you achieve 50x magnification, ideal for detailed lunar observation, scanning the Orion Nebula, or observing the Andromeda Galaxy. The comfortable magnification range makes this an excellent "workhorse" eyepiece for general observing.
Optimal Use Cases
- Wide-field lunar observation and full disk viewing
- Open star cluster observation (Pleiades, Hyades, Double Cluster)
- Large nebulae and extended deep-sky objects
- Milky Way star field scanning
- Initial target location before switching to higher magnification
- Low-power comet observation and tracking
- General-purpose low to medium magnification viewing
Perfect Starting Point for Eyepiece Collections
For beginners building their first eyepiece collection, the Kellner 20mm serves as an excellent foundation. Its moderate focal length provides useful magnification with most telescopes, while the affordable price allows budget allocation for additional eyepieces at different focal lengths. Many experienced astronomers keep a Kellner eyepiece in their collection as a reliable backup or for quick wide-field surveys of the night sky.
Comfortable Viewing Experience
The approximately 15mm eye relief provides comfortable viewing for most observers, including those who wear eyeglasses for astigmatism correction. The rubber eyecup can be folded down to accommodate eyeglass wearers, or kept extended for comfortable eye positioning during extended observing sessions. The eyecup also serves to block stray light from streetlights or other sources, maintaining image contrast during observation.
Filter Compatibility
The integrated filter threads accept standard 1.25″ astronomical filters, allowing you to enhance your observations. Add a moon filter to reduce glare during bright lunar phases, use planetary color filters to enhance contrast on Jupiter or Mars, or attach a light pollution filter for improved nebula visibility from suburban locations. The filter threads provide valuable versatility for different observing scenarios.
Reliable Optical Performance
While the Kellner design is simpler than modern wide-field eyepieces, it delivers honest optical performance with good central sharpness and acceptable edge correction. The 3-element design minimizes internal reflections, providing good contrast on the Moon and planets. For observers primarily interested in lunar and planetary work, or those observing from telescopes with focal ratios of f/8 or slower, the Kellner design performs admirably.
Why Choose Binorum Eyepieces
Binorum eyepieces are designed to make quality astronomy accessible to observers at all experience levels. Each eyepiece is manufactured with careful attention to optical alignment and coated with multi-layer anti-reflection coatings to maximize light transmission. The metal construction ensures mechanical precision and long-term reliability, while strict quality control procedures guarantee consistent performance across the product line. Binorum combines time-proven optical designs with modern manufacturing techniques to deliver exceptional value, allowing both beginning and experienced astronomers to build comprehensive eyepiece collections without breaking the bank. With Binorum, you receive dependable optical performance backed by a commitment to making amateur astronomy equipment accessible to everyone.
