|The Blug or Barlowed collimation plug is an accessory for collimators that allows Barlowed primary mirror alignment. The Blug, short for Barlowed collimation plug, is a new collimation accessory used together with a regular laser collimator to perform Barlowed laser primary mirror alignment. |
The Blug does not attach to the collimator like a self-Barlow attachment. It is inserted in the inner end of the focuser drawtube, inside the telescope tube or upper cage, and it is retained by an O-ring in the base of the Blug. It has an anti-reflection coated negative lens mounted in an axial hole, and a white 45 degree screen face. Blugs are made in two sizes to fit 1.25" and 2" drawtubes.
On a truss tube dob, the 45 degree face of the Blug is easily visible from primary adjustment position. You observe the shadow of the primary mark on the Blug face as you turn the primary adjustment screws to center it.. With a solid tube scope, the Blug can be turned 180 degrees to face the front, and the target shadow seen easily from the front.
The Blug extends 3/8" into the back end of the drawtube, so the laser collimator used with it can not extend past this or it will interfere with the Blug and not allow it to seat properly. A long collimator can often be drawn back in the eyepiece holder and clamped so it will not interfere with the Blug.
I supply a shim kit with the Blug for use if the drawtube inner end is larger than the eyepiece nominal size. The plastic shim strips can be inserted under the o-ring, and in this way drawtubes as much as 1/10" oversize can be accommodated.