90 - Degree Zenith Mirror 1.25 - inch Astronomical Telescope Accessory Internal plane mirror, metal frame, small chromatic aberration. It is used for connection and imaging between the main mirror and eyepiece of refracting and catadioptric astronomical telescopes. It can be used for astronomical telescopes with 1.25 - inch interfaces and can be connected to 1.25 - inch astronomical telescope eyepieces.