Chuck wrote:

Got it now, Don and Kurt. Mental block! Actually it can rotate to any viewing angle and still be useful.

Using the blug with a closed-tube Newt presents some difficulties in seeing the blug from the back-end or primary mirror end of the scope. Here's what I do. 1) Use an extendable automechanic mirror to see down the tube: http://gallery.utahastronomy.com/main.php?g2_itemId=11124 2) Use the secondary "laser halo" to do the last fine tune of the alignment using the primary mirror. This tip isn't in Glatter's instructions; it is something that I homebrewed. The very last final tweak in high-end laser collimation is to get the secondary centered in the laser light cone coming reflecting off the primary. This is most easily seen in a darkened room. If the scope is collimated, the secondary will be framed in a halo of laser light that is concentric. If is off the slightest bit, the laser halo framing the secondary will be off-center and elliptical. I don't have a photograph, but here is a sketch of what the halo looks like when you peer down the front of the closed tube - http://gallery.utahastronomy.com/main.php?g2_itemId=11139 This final tweak is made with a fine adjustment to the primary mirror knobs made while standing behind the primary mirror. So, how do you see the halo with a closed Newt tube when standing behind the primary mirror? I have a couple of techniques. If I am indoors and there is a convenient wall near the scope, just point the open tube towards the wall in a darkened room - the laser halo and secondary shadow will project on the wall. I also have used a piece of paper taped to a tripod and posted in front of the tube - http://gallery.utahastronomy.com/main.php?g2_itemId=11127 - or a pillow case or T-shirt draped over a chair. Although the above picture is in the daylight, this adjustment is usually done in a darkened room or outside at night. I also have some other homebrew tips for lurkers for collimating a fast Newt that depart from the instructions included with Glatter's laser collimators. Glatter's approach is to align everything relative to the flat surface of the top of the focuser tube - using a big carpenters T-square to set the initial positions of the secondary mirror and the primary mirror. Everything is measured relative to the focuser tube top. Glatter's T-square approach proved too cumbersome for me, so I home brewed the following method which emphasizes minimizing collimation errors relative to the center line of the telescope tube. Again, most of this is intended towards collimating and aligning a GEM mounted Newt. It is probably too much effort for truss dob or ordinary box dob. I modified my scope cover by drilling two holes in it - one at the center and one off-axis. http://gallery.utahastronomy.com/main.php?g2_itemId=11130 The black duct tape is used to cover the holes during scope storage. On the front of the tube at the secondary mirror, the cover and the center hole is used to initially rough align the secondary mirror assembly along the telescope tube's central axis. The Cheshire and flashlight are aids to seeing the secondary mirror in the now dark tube. http://gallery.utahastronomy.com/main.php?g2_itemId=11133 On the back of the tube at the primary mirror, the cover, off-axis hole and the straw-depth indicator, are used to initially roughly align the primary mirror perpendicular to the central axis of the telescope tube. http://gallery.utahastronomy.com/main.php?g2_itemId=11136 Then I rough align the secondary mirror in the length dimension along the tube's central axis by visual sighting both within the main tube and by sighting down the focuser tube. The mirror is offset about 1/8" up-tube per Nils Olaf Carlin's article on parallax error in the secondary mirror. This is only done on the first collimation. I do not do this rough alignment during followup maintenance. http://gallery.utahastronomy.com/main.php?g2_itemId=11142 Once these preliminary mirror positions are set, then I use the laser colliminator per Glatter's instructions, except for the home brewed final adjustment mentioned above using the laser halo as a guide. All the adjustments are made to the maximum extent possible only using the secondary mirror. This forces the collimation axis to be co-incident with the central axis of the telescope tube and the primary mirror that is sitting perpendicular to the tube axis. The benefit of this approach, again limited to a GEM mounted Newt, is that the central axis of the tube becomes the fiducial axis for collimation and subsequent cone error correction. When I go to adjust the cone error using the Allen bolts on the mounting bar - http://gallery.utahastronomy.com/main.php?g2_itemId=11145 - I only needed to turn the adjustment bolts at most 1 to 2 turns on a two of the four Allen bolts before cone error is minimized. My Newt now easily adjusts for cone error almost like it was a refractor. For lurkers, some of the above is homebrewed. Use at your own peril. - Kurt ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ