Hi Dindsy.
Yes - that is my problem exactly. Using my (relatively expensive) 12mm EP I can get a very sharp and clear image, but once I introduce the barlow it goes fuzzy. What I have done is to put my EP in the barlow and insert the barlow into the focusser without tightening the screws on the focusser. What I do then is to adjust the focus by moving the barlow in and out until I get a reasonably focussed image, then lock the screws in place. From there I use the focusser to refine. But, having done this I still don't get a sharp image...but my "perception" is that it is better being displaced a little in the focusser.
On the primary mirror issue, yes again that sounds correct. My scope is a SkyWatcher and (again) yes, the book made no mention of removing a cover. I will have a closer look at what you suggested, but my feeling is that the collimation on the scope is pretty good. The secondary mirror was out, so I fixed that up, but it seems to be positioned in the middle of the primary, so collimation doesn't appear to be a problem...I hope!
I'm going to contact the shop I purchased the barlow through for some suggestions; if I get any I will let you know.
Shalom & clear skies,
John
