Posted By David Tandy
I think I already know the answer to my question but I wanted to check here before I spend the $$ only to find out I'm wrong (wouldn't be the first time :S ).
I have built a Newtonian astrograph and the primary is a conical form that mounts to the mirror cell using a post that passes through the 3" diameter core at the center of the mirror. So, there is no optical surface at the center of the primary mirror at which to place a donut or triangle collimation aiming point. See the attached image for a CAD rendering of the scope.
Since the scope is F3.6 collimation is critical and I'd like to use a laser tool. I think the Glatter holographic collimator will work well in this situation but I thought I'd ask for some opinions in this forum.
There is the head of a 1/4-20 screw that is located dead center of the mirror post that I can use as an aiming point for a single beam laser to collimate the secondary. But, since the beam isn't reflected it doesn't help with collimating the primary. My question is this.. Can I use the image of the holographic projection from the Glatter tool that is reflected back on to the face of the laser collimator to collimate the primary? I think this should work but not having seen a holographic collimator in action I'm not positive.