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Bruce,
Yep thats it. Prior to trying to loosen the center screw you need to loosen each of the 3 "collimation screws" a little bit which will then also loosen the center screw. you then adjust the center screw as necessary either loosening or tightening it. If you need to move the secondary further from the primary keep undoing the 3 collimation screws a bit then do the center one up a bit and undo the 3 collimation screws again a little bit and do the center screw up a little again. To move the secondary up or down you sorta work the 3 collimation screws and the center screw together as a pair. The secondary is held in the correct position by the center screw putting pressure in the opposite direction to the 3 collimation screws.
Once you get the secondary in the correct position in relation to the primary you then use the 3 collimation screws only to adjust the secondary tilt. Prior to this step you need the center screw done up with medium pressure so that when the process is finished the 3 collimation screws and the center screw are held fairly firm against each other. Be aware however that the top of some secondary holders is only plastic where the 3 collimation screws rest against so don't go too firm if it is. I actually put a piece of 1.2mm Stainless Steel on the top of my secondary holder for the screws to ride on.
CS-John B
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