The Glatter 2” tuBlug (TUbe with Barlowed laser pLUG) ends the trial and error and walking back and forth between eyepiece and mirror that you go through when trying to collimate your large Newtonian reflector by yourself, with no one to adjust the collimation knobs at the back of the scope while you direct them from the eyepiece. It is also useful if you have a solid tube Newtonian and can’t see the center spot on your primary mirror, or have a big truss-tube Dob but don't have the time to slide your shroud out of the way to see the mirror and then readjust it after collimation.
The 2” tuBlug is a 2” tube with a side cut-out containing an angled white screen with a central aperture, similar to a Cheshire eyepiece. After adjusting your diagonal mirror with an optional 2” laser collimator so that the laser beam strikes the center of your primary mirror, the laser is removed from your telescope focuser and the tuBlug inserted into the focuser. It is turned so that the white screen in the cutout is facing the primary mirror end of your scope. Your 2” laser collimator is then inserted into the tuBlug. The light from your laser passes through a multicoated negative lens (Barlow) in the tuBlug’s central aperture and is projected towards your scope’s optics.
The laser beam is first diverged by the lens in the tuBlug and then reflected by your scope’s diagonal mirror down the tube to illuminate the central area of your primary mirror. The diverged beam is in turn reflected back up the tube by the parabolic primary mirror, which collimates the beam back into parallel rays. The collimation mark in the center of the primary mirror blocks some of the light, so that the upward-traveling beam contains the silhouette shadow of the collimation ring or mark within it.
This returning collimated beam is reflected back by your diagonal mirror onto the white screen of the tuBlug, where the shadow of the collimation mark can be seen from your position at the primary mirror end of the scope. Using your scope’s collimation screws, simply center the collimation mark’s reflected shadow on the center aperture in the white tuBlug screen to collimate your primary mirror.
The 2” tuBlug fits any 2” focuser and can be used with any well-centered 2” laser collimator, such as the 2” Glatter single beam laser collimator #GLC2. The tuBlug also comes in a 1.25” size (#TUBLUG1).
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