Bresser 3x Barlow.

Fully multi-coated achromatic design with edge-blackened lenses for maximum contrast. The Barlow is ideal for use with low-powered (long focal length) eyepieces to deliver higher powers, but with maximum eye-relief and viewing comfort. This excellent-quality all metal high-powered views with a high standard of colour correction at low cost - ideal for planetary and lunar observing. Best performance when used with long focal length eyepieces (10mm and higher).