So I have a 6" Astro-Tech RC scope that's been sitting on my shelf for the last couple of years.
I spent a year or two imaging with it, and it was a fun scope - but collimation is pretty difficult. In the past, I have collimated it using the "hall of mirrors" effect to adjust the primary. It took some time for me to figure out that you can't actually see the reflections properly unless you remove the baffle tube, which requires taking off the front of the telescope to get the secondary mirror out of the way.
Anyway, I had a thought the other day that it might be possible to collimate one of these scopes with a barlowed laser collimator.
I happen to have a nice AstroSystems barlowed collimator, so I pulled the scope off of the shelf and played with it for a while today. To start the process, I put the laser into the focuser without the barlow lens. This sent the beam directly at the secondary mirror. looking through the front of the scope, I was able to see the secondary mark reflected in the primary mirror. I could also see that the beam was not quite centered in the secondary mark. To center the laser beam, I used the primary mirror collimation screws.
This method of adjusting the primary depends on what (in my opinion) is one of the weaker design points on these scopes. Namely, it works because the focuser is attached to the primary mirror mount. If that were not the case, then adjusting the primary collimation screws would not affect the beam at all. I still think that this is a weak point in the design, because a heavy imaging train could slightly pull the primary mirror out of collimation as the scope points in different directions - but hey, this was an experiment, and perhaps I could mount a light weight imaging train for this scope.
After adjusting the primary, I attached the barlow lens to the laser and put it back in the focuser. What this does is diffuses the laser beam such that a reflection is cast back towards the laser emitter with a shadow of the center mark from the secondary. I could use the seconary mirror collimation screws to adjust this, but I didn't need to. The laser emitter was already perfectly centered in center of the reflected mark.
So at this point, I believe that the scope is pretty close to collimated. We don't get many clear nights around here, so I doubt that I'll be able to do a full evaluation anytime soon. But we are forecast for a clear night tomorrow night, so I might throw an eyepiece onto the scope and see what it looks like.
Anyway, I just wanted to throw this out there to see what people think of the idea. It does depend on the secondary mark being accurately centered. It also depends on the focuser being square with the primary mirror. But if those two things are true, then the two mirrors should be pretty accurately aligned with each other at this point.