You may not be able to collimate a cat/sct but I think rider that the laser beam must have some kind of width. The curved secondary (mirror or miniscus) is only tangentally perpendicular to the beam at one (hopefully the central) point. Any photons outside this line, should be reflected away from the source (ie away from the incoming beam) and be spread. This spread maybe wide enough to reach the primary. All of this depends on the level of curvature and the width of the beam. Might be an interesting test. I will get some batteries for my collimator and check it on the sct. I suspect that the red laser light should be visible on some part of the primary mirror. Could anyone check this and save me buying batteries ?
