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Thanks Geoff..I'm sure a few dob owners will find this handy..I learned from collimating my first Dob, (Saxon 200mm), that you could loosen the 3 adjustment grubscrews and the central locking screw to rotate/position the secondary under the focuser..then to tighten the grubscrews a little each time until they seat against the backing plate of the secondary mirror holder..then check it's position under the focuser..if it's not central..it was then easy to loosen off the grubscrews a tad then loosen/tighten the central locking screw to re-position the secondary..then again tighten the grubscrews..it does take a while to do..but then you're dealing with very fine movements...once the secondary is centered..collimating it is just a matter of finely adjusting the grubscrews until they have seated slightly firm and no tighter!!..the allen head of grubscrews can burr if too much force is used!!..for replacement grubscrews you can try Ajax Fasteners..(size 4 x 20 mm) and buy a watchmaker screwdriver set (from some of the $2.00 shops!) which might have an allen screwdriver to fit..makes life easier!!
Cheers!
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