Eyepiece Beta Classic Ortho 18mm 1.25 inch — orthoscopic eyepiece, 18 mm focal length, 1.25" barrel

Beta Classic Ortho 18mm 1.25 inch is an orthoscopic eyepiece designed for visual astronomy. With an 18 mm focal length and a 1.25" barrel, the eyepiece provides moderate magnification and a narrow to medium apparent field of view optimized for high-contrast, sharp images. The orthoscopic optical design reduces edge distortion and spherical aberration, producing crisp views of the Moon, planets and brighter deep-sky targets when paired with an appropriate telescope.

Advantages

The eyepiece offers clear, high-contrast images with minimal field curvature and low chromatic aberration due to its orthoscopic construction. Its 1.25" barrel format ensures compatibility with a wide range of amateur telescopes and diagonal adapters. The 18 mm focal length provides a practical balance between magnification and field of view, useful for both planetary detail and general observing sessions. Mechanical construction is compact and straightforward, suitable for regular field use.

Suitable for

• Planetary observation (Moon, Mars, Jupiter, Saturn)
• Lunar surface detail and terminator studies
• Brighter deep-sky objects where higher contrast is beneficial
• General visual observing and outreach with small to medium telescopes

Key specifications

• Optical design: orthoscopic eyepiece
• Focal length: 18 mm
• Barrel diameter: 1.25 inches
• Intended use: visual astronomy, high-contrast observing
• Field performance: minimal edge distortion and low field curvature

How to use

Insert the 1.25" barrel securely into the telescope focuser or diagonal and tighten the retaining thumbscrew to prevent rotation. Allow the telescope to reach thermal equilibrium for stable images, then focus the eyepiece using the focuser knob until fine detail is resolved. For planetary observing, use accurate tracking or short manual corrections to keep the target centered; for deep-sky viewing, use averted vision to detect fainter structure. Swap to higher- or lower-focal-length eyepieces as needed to compare magnifications and field of view.

Usage recommendations

Use the eyepiece with telescopes that provide a focal ratio suitable for orthoscopic designs (commonly f/6 and slower) to minimize off-axis aberrations. Clean optical surfaces with a soft blower and microfiber cloth only when necessary, and store the eyepiece in a dry, dust-free case to preserve coatings and mechanical integrity.