Binorum Plössl 12.5mm 50° 1.25″ Eyepiece
The Plössl eyepiece design has been a favorite among amateur astronomers for decades, and for good reason. The Binorum Plössl 12.5mm represents this time-tested optical formula at its best - a simple yet ingenious four-element construction that delivers bright, high-contrast images at an affordable price point accessible to every observer. We believe this is one of the finest eyepieces available in this price category.
Classic Four-Element Plössl Design
The Plössl optical configuration employs just four lens elements arranged in two matched pairs (doublets), creating a symmetrical design that has proven its worth over generations of astronomical observation. This elegant simplicity offers several advantages:
High light transmission: With only four air-to-glass surfaces requiring anti-reflection coatings (compared to six or more in complex wide-field designs), Plössl eyepieces inherently transmit more light and suffer less from internal reflections. Every surface features multi-layer broadband coatings to maximize brightness and contrast.
Excellent color correction: The matched doublet design effectively controls chromatic aberration, ensuring stars appear as crisp white points rather than colored blurs, and planetary images display true colors without distracting fringing.
Sharp field performance: Plössl eyepieces are particularly noted for maintaining good edge sharpness even when used with fast focal ratio telescopes (f/5 and faster). This means you see sharp star images across the entire 50° apparent field, not just at the center.
Versatile 12.5mm Focal Length
The 12.5mm focal length positions this eyepiece as an excellent medium-power workhorse for a wide range of observing applications. It provides comfortable magnifications with common telescope focal lengths:
- 500mm telescope: 40× magnification
- 750mm telescope: 60× magnification
- 1000mm telescope: 80× magnification
- 1250mm telescope: 100× magnification
This magnification range is ideal for observing lunar craters and mountain ranges, planetary disks and their major features, star clusters, brighter nebulae, and galaxies. The 12.5mm serves as the perfect "middle ground" eyepiece between low-power wide-field views and high-power planetary observation.
Comfortable 50° Apparent Field
The 50° apparent field of view represents the traditional Plössl specification - wide enough to provide comfortable, immersive viewing without the complexity and cost of ultra-wide designs. This field angle strikes an excellent balance for general astronomical observation, giving you enough field to appreciate the context around your target while maintaining the optical simplicity that delivers crisp, contrasty images.
Thoughtful Mechanical Design
Fold-down rubber eyecups: Soft rubber eyeguards provide a comfortable cushion for your eye while blocking stray light from the sides that could reduce contrast. The eyecups fold down easily for eyeglass wearers, allowing them to position their eye at the correct distance to see the full field of view.
Quality metal construction: The eyepiece barrel is precision-machined from metal rather than plastic, ensuring long-term durability and dimensional stability. The anodized finish resists scratches and corrosion, while the internal surfaces are blackened to suppress reflections.
Filter threads: Standard 1.25-inch (M28.5 × 0.6) filter threads are incorporated into the base of the barrel. Simply screw on a moon filter to reduce lunar glare, a nebula filter to enhance emission nebulae, or planetary color filters to bring out atmospheric details - the choice is yours.
Universal 1.25-inch barrel: The industry-standard barrel diameter ensures compatibility with virtually every modern telescope focuser, diagonal, and accessory on the market.
Performance with Fast Telescopes
These eyepieces demonstrate notably good edge definition even when used with "fast" f/5 telescopes. You may be familiar with this concept from camera lenses: the lower the f-number, the greater the telescope's light-gathering ability and the "faster" it is considered. F/5 telescopes are among the fastest commonly used in amateur astronomy.
Fast focal ratios can challenge eyepiece performance because the converging light cone is steeper, making optical aberrations more difficult to correct. Many budget eyepieces show significant field curvature or coma (elongated star images) at the field edges when used with f/5 systems. The Binorum Plössl 12.5mm maintains good sharpness across its field even under these demanding conditions, making it suitable for use with Newtonian reflectors, fast refractors, and other telescope designs.
Recommended Applications
- Lunar observation: Perfect magnification range for exploring crater fields, mountain ranges, and mare regions in detail
- Planetary viewing: Shows planetary disks clearly with major features visible - Jupiter's cloud belts, Saturn's rings, Mars' polar caps
- Open star clusters: The 50° field nicely frames clusters like the Pleiades or Double Cluster
- Globular clusters: Sufficient magnification to begin resolving individual stars in bright globulars like M13
- Brighter nebulae: Good for observing emission nebulae, especially when combined with a nebula filter
- Galaxy observation: Suitable for brighter galaxies like M31 (Andromeda), M51 (Whirlpool), and M81/M82
Technical Specifications
- Optical design: 4-element symmetrical Plössl (two cemented doublets)
- Focal length: 12.5mm
- Apparent field of view: 50°
- Barrel diameter: 1.25 inches (31.7mm)
- Coatings: Multi-layer broadband anti-reflection on all air-to-glass surfaces
- Eye relief: Approximately 10mm (comfortable for most observers)
- Filter threads: Yes, standard 1.25-inch (M28.5 × 0.6)
- Barrel material: Anodized metal
- Eyecup: Fold-down rubber design
- Internal finish: Blackened to reduce reflections
- Dust caps: Included for both ends
Exceptional Value
The Binorum Plössl 12.5mm delivers performance that punches well above its price point. The combination of proven optical design, quality construction, and practical features like filter threads and fold-down eyecups makes this eyepiece an outstanding choice for beginners building their first eyepiece collection and experienced observers seeking reliable, affordable optics.
While more expensive eyepiece designs may offer wider fields or longer eye relief, the Plössl's fundamental optical excellence and mechanical simplicity ensure it remains relevant regardless of your experience level or the sophistication of your telescope. Many veteran astronomers keep Plössl eyepieces in their collections precisely because they deliver consistently excellent views with minimal fuss.
Why Choose Binorum
Binorum focuses on providing amateur astronomers with reliable, well-made equipment at honest prices. The Plössl 12.5mm exemplifies this philosophy - no marketing gimmicks, just solid optical and mechanical design executed with care. Each eyepiece is quality-controlled to ensure proper lens alignment, coating quality, and mechanical fit. When you choose Binorum, you're choosing equipment designed by observers who understand what really matters for successful nights under the stars.
