The current Feathertouch focuser has a 2" filter thread at the inner end of the drawtube, with a large relief diameter past the thread. In order to fit this focuser, Howie Glatter supplies all 2" Blugs with an adapter o-ring which fits on the end of the Blug and acts as a "spacer" so that the Feathertouch focuser threads will engage the Blug retention o-ring. However, for those who will be using the Blug primarily with a Feathertouch focuser, he now produces a Blug that will fit the Feathertouch directly without using an adapter. It is called the Flug. The only difference between the Blug and Flug is that the retention o-ring on the Flug is right up against the Flug shoulder. The Flug will also fit fine in most regular 2" drawtubes.
Blug is short for Barlowed collimation plug. Used with the Howie Glatter Laser Collimator (not included), this is a new collimation accessory for performing highly accurate Barlowed laser alignment of the primary mirror in Newtonian telescopes.
The Blug is inserted in the end of the focuser drawtube, inside the telescope tube or upper cage, and is retained by an O-ring in its base. An anti-reflection coated negative lens is mounted in an axial hole, and a white 45-degree screen is on the Blug's face.
On a truss tube Dobsonian, the 45-degree face of the Blug is easily visible from the adjustment position of the primary mirror. Simply turn the primary mirror adjustment screws to center the shadow of the primary mark on the Blug face. The Blug can be turned 180 degrees to face the front of a solid tube scope and the target shadow is easily seen from the front.
The Blug extends 3/8" into the back end of the focuser drawtube so the laser collimator used with it can't extend past this or the Blug will not seat properly. A long collimator can usually be drawn back in the eyepiece holder and clamped so it will not make contact with the Blug.
With this 2" version of the Blug, shims are included for when the drawtube inner end is larger than the nominal eyepiece size. The plastic shim strips can be inserted under the O-ring and, as a result, drawtubes oversize by as much as 1/10" can be used effectively.
Adjust the secondary mirror angular alignment as usual, and place the laser spot in the center of the collimation target on the primary. Remove the aperture stop from the collimator for Barlowed collimation to allow as much light as possible through the Barlow lens. This produces the highest shadow contrast.
Insert the Blug into the inner end of the focuser drawtube and make sure it seats firmly against the tube edge so that there is no danger of it falling out. Reinsert the focuser drawtube and adjust the primary mirror to center the collimation target shadow on the Blug face. Remove the collimator and Blug and you are done.