Skyliner 300P 12" Dobsonian (Solid-tube)

[ajohnson]

I also have a 300PDS, although mine is on an NE6 mount, mine was from an e-bay seller who knew little about it (or more accurately less than I did!) and is missing some parts. I have noted a small issue when carrying and slewing the scope, as you go from side of the meridian to the other there is a soft but noticeable "clunk" as the primary mirror moves. After some looking I have noted this is due to the mirror mount and cell moving in the main holder. I.E. the mirror cell doesn't move but even with collimation screws and lock screws tight the 3 point collimation web / mirror mount can move a couple of mm. Any suggestions for curing or reducing this?

[ajohnson]

Be carefull not to tighten the mirror retaining clips, these mirrors are quite thin and any pressure can lead to astigmatism. You should be able to slide a piece of printer paper between the mirror face and the clips.

Just tried this on my 300PDS, sheet of paper! more like a magazine. I have a huge gap between my clips mirror the plates rattle a couple of mm each way. This may be the actual problem. I will investigate further.