The 2-element design uses special glasses to preserve the fine color correction of the main objective. The optical elements are hand-corrected and precision centered to insure that no aberrations are introduced into the system. The Barlow focal length is 127 mm which is longer than conventional types. This minimizes the divergence of the edge rays and therefore reduces the apparent vignetting common in many eyepieces (Plossls and Panoptics). The Barlow features a brass locking ring as described for the 2.7" focuser. Note the following positions and resulting magnifications:

1.7x after the diagonal
2x before the diagonal or camera adapter
2.4x before the Baader Planetarium Binocular Viewer (threaded directly into the prism diagonal)
3.2x before the Baader Planetarium Binocular Viewer used with the extension