Refractor telescope Skywatcher BK 102/500 OTA — 102 mm aperture, 500 mm focal length

The Skywatcher BK 102/500 OTA is a refractor telescope optical tube assembly with a 102 mm aperture and a 500 mm focal length (f/4.9). Its compact, lightweight design makes it suitable for field use and portable observing sessions. The fast focal ratio and wide field of view are tuned for visual observation of the Moon, planets and brighter deep-sky objects, and the OTA format allows pairing with a variety of mounts and cameras for basic astrophotography when a compatible mount and accessories are used.

Advantages

The BK 102/500 OTA combines a relatively large 102 mm objective with a short 500 mm focal length to deliver wide-field views with good light gathering for its size. The refractor optical design requires minimal collimation and provides stable, high-contrast images for planetary detail and lunar observing. Its compact tube and modest weight simplify transport, setup and use on smaller mounts. The f/4.9 focal ratio enables shorter exposure times for basic astrophotography when paired with a tracking mount and appropriate camera.

Suitable for

• Visual observation of the Moon and planets
• Wide-field views of bright deep-sky objects such as open clusters and large nebulae
• Portable field observing and outreach events
• Basic astrophotography with a compatible equatorial or tracking mount

Key specifications

• Aperture: 102 mm
• Focal length: 500 mm
• Focal ratio: f/4.9
• Optical type: Refractor (achromatic design)
• Format: OTA (optical tube assembly) — no mount or tripod included
• Recommended use: Visual observing and basic astrophotography with compatible mount

How to use

Attach the OTA to a stable mount compatible with the tube ring or dovetail, balance the assembly and align the mount according to the mount manufacturer’s instructions. Start with low-power eyepieces to locate targets using the wide field of view, then increase magnification for planetary or lunar detail. For astrophotography, secure a camera with the appropriate adapter, ensure accurate polar alignment if using an equatorial mount, and use guiding or short exposures to reduce star trailing. Always allow the instrument to thermally acclimate outdoors for improved image stability.

Recommendations

Use this OTA on a stable equatorial or motorized alt-azimuth mount for best results. Pairing with low- to medium-power eyepieces emphasizes the telescope’s wide-field strengths; for photography, select a camera and adapters suited to short focal lengths and consider field flattening or focal reducers if required.