Posted by Robin Vann at 20:48 on 2010 Sep 06
Thank you for your reply, David, and excuse me for being such a rank beginner.I have always had difficulty doing star tests, never really achieving the Airy disc pattern, possibly due to the inadequacies of the rack and pinion focuser on my Skywatcher 150mm. However, Jupiter is sharp as a button, as was a shadow transit of Io last week, Io’s shadow being pin sharp.So I guess I can leave it for now.To be absolutely accurate, I think the problem is that I haven’t perfectly centered the collimator’s cross-hairs over the centre marker on the primary at stage 2 (the centre diagram).Thanks again :)Robin Vann