Howie Glatter Blug – The insert for convenient adjustment.
The Blug stands for Barlowed Collimation Plug.
The Blug is a 45° wedge that makes the reflected markings and concentric circles of the laser from the main and secondary mirrors visible. The barlow lens is built directly into the "Blug" and has an anti-reflective coating.
What does the "Blug" do?
On a truss tube Dobsonian, the image of the 45° wedge of the Blug can be easily recognised during adjustment of the primary mirror. You only need to follow the shadow image of the concentric circles and the centre mark to adjust the mirrors to the optical axis. With a full tube, the "Blug" must be rotated 180° outwards to see the images.
