Puzzled and amazed and how simple life can be....at least for now. At lunch, went home and plugged in the Glatter with the 1 mm stop and centered it as carefully as I could in the focuser and then centered the laser in the triangle with the secondary screws and then got the little red rabbit back in the hole it came out of with the primary knobs and it appeared that there were concentric circles (similar to a star collimation) around the center hole of the 1mm. Then put in the Blug and it was centered (or very close to such). Put in the Catseye AC and it was the best image I've seen. Everything seemed centered and no ghost triangles. Then put in the TuBlug and it was also giving a good test. Now to mess it all up tonight and try it again. It seems that if I can do it repeatedly all with the 1 mm stop, then all this will seem very simple. I wonder how easy it would be to see the 1mm stop from the back of a truss, maybe even in the secondary?
Just remember to compare what you see with the Blug until you really get the hang of seeing the diffraction rings and centermark shadow. The return beam of the laser by itself, diffraction circles notwithstanding, isn't the best way to line up a primary. Though, admittedly, if the alignment of the primary is way off, the return beam of the unbarlowed laser will at least put you in the ballpark for easy collimation of primary tilt with the BLUG or barlow attachment.
I've seen many people in the field collimate their primaries with the return beam of a single beam laser. So it might be worthwhile to mention why
the return beam of a simple laser isn't up to the task of collimating a primary.
Let's say you adjust the secondary to put the laser beam outside the primary's centermark. Could you adjust the tilt of the primary to return the beam to its source on the bottom of the laser? Yes. Would the telescope be collimated? No. The point is, there will be some error in having the laserbeam hit the center of the primary, but you can always adjust the primary to return the beam to its source. And, with most lasers, estimating the center of the primary's mark to the necessary degree of precision isn't possible because the eye is either too far away, the beam is too bright, or the beam shape isn't small enough to accurately assess the center of the mirror closely.
Now if the beam hits exactly
in the center of the primary, the return beam will hit the source in a perfectly collimated scope.
So how can you tell if you're compensating for an inaccurate centering of the laser with a tilt error in the primary? Well, one way is the cheshire. Another way is the barlowed laser technique of Nils Carlin. Another way is a Krupa collimator. And, another way is to reduce the aperture of the laser until the laser beam has a diffraction pattern where it hits the primary (the small size of the beam, coupled with the diffraction pattern, makes estimating dead center a lot easier).
This last way, as some have discovered, results in a return beam from the primary to the laser that not only contains the diffraction rings around the central laser beam itself, but also the shadow of the primary's centermark within the diffraction pattern--in essence, similar to what you would see with a barlow. So you can center the shadow, as you'd do with a barlow.
Of course, the fact the laser is not diffused, as with a barlow, means that shadow is a little harder to see and center. But, as Vic has found out, this works quite well and gets you quite close to perfect collimation quite quickly.
It goes without saying the laser must be accurately collimated, and have a very small aperture stop (1mm or less).
I've done some experimenting with an accurate laser with a 0.8mm aperture stop, comparing it to the Catseye TeleTube sight tube, and I get nearly equal accuracy with either. I actually looked at the primary from up close (shroud lifted) when using the laser, and used a diffraction point in the crosshairs to center in the primary's centermark.
[a little discussed characteristic of vision is that when the sight tube's crosshairs are thin and at a non-focused distance from your eye, the crossing point produces a diffraction "dot" that you can center in the primary's mark for greater accuracy].
De-collimating and aligning with either method gave me equal results when checked later with the autocollimator.
We are becoming blessed with an abundance of good techniques in collimation. What we need to do is keep harping about the use of collimation caps and inaccurately-collimated cheap lasers with 45 degree windows. There is no reason these tools could not be made better with a little more care on the part of the manufacturers. For now, though, we have a handful of companies producing good tools, and that is probably enough.